338 files changed, 677 insertions, 676 deletions
diff --git a/mcs/class/Accessibility/Accessibility-net_4_x.csproj b/mcs/class/Accessibility/Accessibility-net_4_x.csproj
index fd221399b4f..a89d8143812 100644
--- a/mcs/class/Accessibility/Accessibility-net_4_x.csproj
+++ b/mcs/class/Accessibility/Accessibility-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj b/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
index 48b88be0431..34a588859f5 100644
--- a/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
+++ b/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj b/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
index c6c6e1d98a9..f14a0f64a71 100644
--- a/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
+++ b/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj b/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
index 0a696e99327..5fad3892796 100644
--- a/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
+++ b/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
index 0f986fa7edb..dfdd6e51294 100644
--- a/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
index e728ab3b6be..64deb2b9386 100644
--- a/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
index d03223da7a8..2a6ca08d6bd 100644
--- a/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj b/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
index 5fbdffac13f..004e221444b 100644
--- a/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
+++ b/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj b/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
index 94e3fb7b845..6be187fd8fa 100644
--- a/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj b/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
index 7b85c3e62d1..67482273049 100644
--- a/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj b/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
index 0139b9bd847..488b07377fe 100644
--- a/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj b/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
index d4036639e35..c38bc78d627 100644
--- a/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
index 7db7b11f3e4..c24d0a8ef44 100644
--- a/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
index 86495ec6ef9..1ca5cd352c3 100644
--- a/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
index 5bf4348f408..2f5ae32bc5f 100644
--- a/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
index 2d45acd839d..68c77706ec6 100644
--- a/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
index 5585d94392f..37dceddb685 100644
--- a/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj b/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
index bf1049017bb..3f319168f65 100644
--- a/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
+++ b/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj b/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
index d7cb0664af2..ff454640198 100644
--- a/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
+++ b/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj b/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
index e72948c72a5..1b1d3874e62 100644
--- a/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
+++ b/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
index 6f07c8ed413..f9fc30dd5af 100644
--- a/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
index 68967b4623c..5d25b1d51c0 100644
--- a/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
index de0bde861a2..82e6bcf511a 100644
--- a/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
index c7190e6c42f..aea80324732 100644
--- a/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
index 8023d49f5d4..cb7ceff0a62 100644
--- a/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
index 0bf8f79ed4c..a9344fd6d90 100644
--- a/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
index 5f110019deb..2eb477411d8 100644
--- a/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
index 711bbc3b229..eedd8d3f1b5 100644
--- a/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
index 73d07be051d..3e14d96ab54 100644
--- a/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
index 3e15f174887..c6a74b21cfb 100644
--- a/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
index 2b4548a61cd..1ce6eba7c33 100644
--- a/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj b/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
index e4f7cb1d836..71f2e2b7c4b 100644
--- a/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj b/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
index 96fbeaa2731..344a0be57e7 100644
--- a/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
index 84edae66afc..94aa368c905 100644
--- a/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj b/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
index 7bffad4ac7a..6743bc09f4a 100644
--- a/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj b/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
index 7174faab98b..6ea6b8e04c9 100644
--- a/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
index 1e1198e6fa0..4f2fcc0768a 100644
--- a/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
index 0ad0ed1ed74..dec0d7c1457 100644
--- a/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
index 75f4a5c3af7..2c537bed7d6 100644
--- a/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
index debfb50b98e..fafa6041e56 100644
--- a/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
index 86de8ebe7bc..8258fe15f4b 100644
--- a/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj b/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
index bba51cf28de..a210d33c68c 100644
--- a/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj b/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
index 807bc7bd1b6..51ee564603c 100644
--- a/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj b/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
index 21b7deedaff..7a7b38ae59b 100644
--- a/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj b/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
index 3196270a436..ca6cd3c7927 100644
--- a/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj b/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
index 8112200bfc1..18743492350 100644
--- a/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj b/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
index c9277839744..132108b9640 100644
--- a/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj b/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
index 6655eab217a..dfad598d73e 100644
--- a/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj b/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
index de3dfb1d69f..28d28e77062 100644
--- a/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj b/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
index 252acf66dfe..774d9582bbe 100644
--- a/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj b/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
index 3a4a2a5827b..f7402e84077 100644
--- a/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj b/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
index 476d6bd4734..400ecbc6138 100644
--- a/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj b/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
index 19a14774883..85667769236 100644
--- a/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj b/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
index 171f55ec7f3..61f18a3e288 100644
--- a/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj b/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
index 50e8e0d50a0..e1c3218235d 100644
--- a/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj b/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
index 3cd38f1ac28..6349a592e5e 100644
--- a/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
index 7ef5d8a92a6..8b13afa7655 100644
--- a/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj b/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
index 7395951b477..df1d534a9d6 100644
--- a/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj b/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
index 085c43d768a..d550b63b9c0 100644
--- a/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj b/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
index 7e1aec5cdbc..ad513e3a281 100644
--- a/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj b/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
index f4b40ff7efb..38b5971f8e0 100644
--- a/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj b/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
index 3e8cfe72934..572c84d81e3 100644
--- a/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
@@ -35,7 +35,7 @@
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     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj b/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
index 018159f693d..69421ecba51 100644
--- a/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
@@ -35,7 +35,7 @@
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     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj b/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
index 6651717a1f4..76914151d26 100644
--- a/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj b/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
index 1fd05626f2c..fe4ac506535 100644
--- a/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj b/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
index 5cbea78a42f..2e3834af7dd 100644
--- a/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
+++ b/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
index 149fea9d6b4..414c011c60f 100644
--- a/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
index 72fd0a488e4..b208945677a 100644
--- a/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
index 9130c9e3735..ed8254c4011 100644
--- a/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
index e14eb089c27..6de8bfa6066 100644
--- a/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
index 703795e2ea4..115cc313209 100644
--- a/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj b/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
index cdee9d8978d..4a9fa29cb66 100644
--- a/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj b/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
index fcf5ab6b0b3..c119bfa86c9 100644
--- a/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj b/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
index eef442d898d..04c460b0467 100644
--- a/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
+++ b/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj b/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
index 5f84ea426b8..108ecc7d3fa 100644
--- a/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
+++ b/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj b/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
index c90090b4e7c..ab838b7f186 100644
--- a/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
index 9539a89ae5b..539bb837668 100644
--- a/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
index f40830292c6..4e3013fd1fb 100644
--- a/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
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     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
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     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj b/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
index 8d4a409e8b6..db54b6e32fa 100644
--- a/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
@@ -35,7 +35,7 @@
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     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj b/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
index 932f862a6ce..c03f30fdd9f 100644
--- a/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
index 13241b75b4c..4cafb05ea44 100644
--- a/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
index 54a91fc8577..c7a078647a4 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
index 2828c2b5196..b8bce8c0882 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
index 0a5d507e745..6f12762a084 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj b/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
index 278c40f9ed2..f96d9463ded 100644
--- a/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
index e98f79e69b2..1c53ec7096d 100644
--- a/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj b/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
index b74d68f392f..08c4615c991 100644
--- a/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
index 0f4738319e1..f833e15be8c 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
index bfb254f69e8..b95a98298d0 100644
--- a/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
index 8f13c5853fc..9e5162f181e 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
index 23c76a7983e..3ad09ebb21f 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
index d1779a93860..a72322415d6 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
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     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
index a1c783ceb13..75d2a8aa30d 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
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     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
index 3d82ca223cb..990d48cef6e 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
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     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
index eb496561a0b..a3b6e5c41bd 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
index d6ff1552992..2ae1af18a02 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
index 70cfd1784b5..cf6fdf5e251 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
index bb036447e85..c44e29551f5 100644
--- a/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
index b889088a62c..de8e5c298be 100644
--- a/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
index 43b8bf706a2..610c83ac1f5 100644
--- a/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
index 270f5b75f16..867d8aee685 100644
--- a/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj b/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
index ae4b0551bae..b4cbc3f3fe9 100644
--- a/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj b/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
index a47887a8fbf..24203d812ef 100644
--- a/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj b/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
index 128db04c4be..16634168cfd 100644
--- a/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
index 363b92da6ae..1d6137cb6ad 100644
--- a/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
index d27ee7f6055..9dd98cf7087 100644
--- a/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
index 57b0ad3ff71..67500f4dfdb 100644
--- a/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
index f7c6c430ecf..7e1de80dd7a 100644
--- a/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
index e7cca6e2380..3e34aaf400b 100644
--- a/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj b/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
index 070a3608c17..a9466ff6014 100644
--- a/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
index a79c56c2d5f..3606386e9f0 100644
--- a/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
index 1cd77eacd7f..f8811bef275 100644
--- a/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
index 9d5d2c082e1..074dace38ee 100644
--- a/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj b/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
index 24f19287af9..e315497957e 100644
--- a/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
index 91aa53608c8..0bba121d612 100644
--- a/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj b/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
index 0c445e053c2..fa22119d637 100644
--- a/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj b/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
index cdbf099ff11..57f9afb53a3 100644
--- a/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj b/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
index 39f7dadaba2..4140c653ae9 100644
--- a/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj b/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
index bc68d0622f3..28c8b98a2da 100644
--- a/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj b/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
index 9dbe04cf29f..8aaadebe489 100644
--- a/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj b/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
index 1cfca01dd37..f7e7553f42f 100644
--- a/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj b/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
index b2caef672c9..862d8697f5c 100644
--- a/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj b/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
index 086fbad7282..556db980722 100644
--- a/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
+++ b/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj b/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
index a5638ed252f..04922f905bf 100644
--- a/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
index 33774c92fdf..f146eb6d9de 100644
--- a/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
index 2dc9c4b2fa2..566d2614ff1 100644
--- a/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj b/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
index 7dd19a8bf0c..12221fbcda8 100644
--- a/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
index 5992134879b..1f5da242c7e 100644
--- a/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj b/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
index ba4e450ad24..54532c6194e 100644
--- a/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
index c42dc69c01a..d2a7c03131c 100644
--- a/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj b/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
index 8605826e178..5a88e547a89 100644
--- a/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
+++ b/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1616,1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1616,1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj b/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
index 017b6202d63..bfbac3c1d59 100644
--- a/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
+++ b/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/Common/I18N-net_4_x.csproj b/mcs/class/I18N/Common/I18N-net_4_x.csproj
index 278fd51f7ef..d18bebbf9a4 100644
--- a/mcs/class/I18N/Common/I18N-net_4_x.csproj
+++ b/mcs/class/I18N/Common/I18N-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>DISABLE_UNSAFE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj b/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
index 793732fa7cf..c784288775c 100644
--- a/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
+++ b/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj b/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
index eabe6115f1f..12558334d59 100644
--- a/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
+++ b/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj b/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
index 9e2104c6baf..f4710197553 100644
--- a/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
+++ b/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/I18N/West/I18N.West-net_4_x.csproj b/mcs/class/I18N/West/I18N.West-net_4_x.csproj
index e2dc1f77714..d42bcb592c1 100644
--- a/mcs/class/I18N/West/I18N.West-net_4_x.csproj
+++ b/mcs/class/I18N/West/I18N.West-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj b/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
index 45b84b40fd9..d0302c1fab3 100644
--- a/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
+++ b/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj b/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
index 73b2b5499b3..2d8da0ef4c5 100644
--- a/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
+++ b/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj b/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
index 46bdc5c9c97..8627bbf3179 100644
--- a/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj b/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
index 347c977d49f..d3dc6c7e922 100644
--- a/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj b/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
index ca5a6616106..92651115536 100644
--- a/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj b/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
index ac4b41052ca..43177e01c0b 100644
--- a/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj b/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
index 472d7267986..da492d9d2c4 100644
--- a/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MICROSOFT_BUILD_DLL</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MICROSOFT_BUILD_DLL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MICROSOFT_BUILD_DLL</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MICROSOFT_BUILD_DLL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj b/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
index e764b1041be..7082da4ac4e 100644
--- a/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
+++ b/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj b/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
index d7439fb7ba5..219a1b45f78 100644
--- a/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
+++ b/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj b/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
index 4607bebc0ed..45c168d4a34 100644
--- a/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
+++ b/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj b/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
index d0dad03159a..8c2860172ff 100644
--- a/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
+++ b/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1030</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SECURITY_DEP</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SECURITY_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1030</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SECURITY_DEP</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SECURITY_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj b/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
index 4a542324d6e..ef4a5827827 100644
--- a/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
+++ b/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,169,219,414,1030,3001,3005,3006</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,169,219,414,1030,3001,3005,3006</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj b/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
index bcf9c8dc840..4ce17372045 100644
--- a/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
+++ b/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_FEATURE_THREAD_ABORT</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_FEATURE_THREAD_ABORT</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_FEATURE_THREAD_ABORT</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_FEATURE_THREAD_ABORT</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj b/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
index 96bd5f8e9c1..efc1e8653dc 100644
--- a/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
+++ b/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj b/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
index d2ed9a93716..3c957e7a277 100644
--- a/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
+++ b/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CECIL</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CECIL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CECIL</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CECIL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj b/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
index 5589b9bcbb1..8ac16535ecc 100644
--- a/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
+++ b/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj b/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
index b6d1fa59030..d423caf8f7c 100644
--- a/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
+++ b/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj b/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
index c9f05a89b4b..b2b2f20e756 100644
--- a/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
+++ b/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj b/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
index 1254cc06180..4b865fff089 100644
--- a/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
+++ b/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SQLITE_STANDARD</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SQLITE_STANDARD</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SQLITE_STANDARD</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SQLITE_STANDARD</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj b/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
index f1b7b066fb0..0b36e7aee6d 100644
--- a/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
+++ b/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj b/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
index d54235f6fba..82f953be77d 100644
--- a/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
+++ b/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_DATACONVERTER_STATIC_METHODS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_DATACONVERTER_STATIC_METHODS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_DATACONVERTER_STATIC_METHODS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_DATACONVERTER_STATIC_METHODS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj b/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
index a5df610f32a..5fb1b2d3166 100644
--- a/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
+++ b/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj b/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
index 59ea8b4165a..25dbdea501c 100644
--- a/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
+++ b/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj b/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj
index 9f366d528ef..b962ddf1572 100644
--- a/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj
+++ b/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj b/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
index 0601c5d3a8e..0a9eccf6f5a 100644
--- a/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
+++ b/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj b/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
index a7efaccc465..2f90a7d766c 100644
--- a/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
+++ b/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj b/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
index 63fd3801afe..6cd87f20764 100644
--- a/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
+++ b/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_MONO_PARALLEL</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_MONO_PARALLEL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_MONO_PARALLEL</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_MONO_PARALLEL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj b/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj
index 6ee0408cb9a..e2ec3604627 100644
--- a/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj
+++ b/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618,612</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618,612</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj b/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj
index 0cda89890d9..8d8c2007af8 100644
--- a/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj
+++ b/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj b/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj
index 05e68c7920c..f41179b86f9 100644
--- a/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj
+++ b/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1030,3009</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1030,3009</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj b/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj
index c5517987025..a5df7f75d8d 100644
--- a/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj
+++ b/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj b/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj
index aead56faff3..b8b784a828d 100644
--- a/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj
+++ b/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj b/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj
index 954a72a07ea..00814ba168b 100644
--- a/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj
+++ b/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj b/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj
index 9d4df7a94a9..131597d19ed 100644
--- a/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj
+++ b/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj b/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
index e2c1501046c..8e20cee020d 100644
--- a/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
+++ b/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,612</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,612</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/PEAPI/PEAPI-net_4_x.csproj b/mcs/class/PEAPI/PEAPI-net_4_x.csproj
index 2d49010632f..b23724821aa 100644
--- a/mcs/class/PEAPI/PEAPI-net_4_x.csproj
+++ b/mcs/class/PEAPI/PEAPI-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj b/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
index d1798aeeabe..c4ee94a44a9 100644
--- a/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
+++ b/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj b/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
index bd323823c2e..6f54fbacd79 100644
--- a/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
+++ b/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj b/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
index 9f491b1182c..7a0a45bde28 100644
--- a/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
+++ b/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj b/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
index d8f4a107402..a1a4b40d890 100644
--- a/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
+++ b/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,219,414,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CLR40;USE_ECMA_KEY;FEATURE_REFLECTIONCONTEXT;FEATURE_REFLECTIONFILEIO;FEATURE_SERIALIZATION;FEATURE_SLIMLOCK</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CLR40;USE_ECMA_KEY;FEATURE_REFLECTIONCONTEXT;FEATURE_REFLECTIONFILEIO;FEATURE_SERIALIZATION;FEATURE_SLIMLOCK</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,219,414,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CLR40;USE_ECMA_KEY;FEATURE_REFLECTIONCONTEXT;FEATURE_REFLECTIONFILEIO;FEATURE_SERIALIZATION;FEATURE_SLIMLOCK</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CLR40;USE_ECMA_KEY;FEATURE_REFLECTIONCONTEXT;FEATURE_REFLECTIONFILEIO;FEATURE_SERIALIZATION;FEATURE_SLIMLOCK</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj b/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
index 52af9c65be9..7597c27f9d7 100644
--- a/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
+++ b/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj b/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
index 06e6c1f8b53..40324c205fa 100644
--- a/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
+++ b/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj b/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
index 6a40087a8f5..7160ec3790d 100644
--- a/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
+++ b/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Core/System.Core-net_4_x.csproj b/mcs/class/System.Core/System.Core-net_4_x.csproj
index 0fd1aeb4358..6dd8ae93203 100644
--- a/mcs/class/System.Core/System.Core-net_4_x.csproj
+++ b/mcs/class/System.Core/System.Core-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_PAL;PFX_LEGACY_3_5;FEATURE_NETCORE;INSIDE_SYSCORE;LIBC;NET_3_5;FEATURE_COMPILE;FEATURE_COMPILE_TO_METHODBUILDER;FEATURE_PDB_GENERATOR</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;PFX_LEGACY_3_5;FEATURE_NETCORE;INSIDE_SYSCORE;LIBC;NET_3_5;FEATURE_COMPILE;FEATURE_COMPILE_TO_METHODBUILDER;FEATURE_PDB_GENERATOR</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_PAL;PFX_LEGACY_3_5;FEATURE_NETCORE;INSIDE_SYSCORE;LIBC;NET_3_5;FEATURE_COMPILE;FEATURE_COMPILE_TO_METHODBUILDER;FEATURE_PDB_GENERATOR</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;PFX_LEGACY_3_5;FEATURE_NETCORE;INSIDE_SYSCORE;LIBC;NET_3_5;FEATURE_COMPILE;FEATURE_COMPILE_TO_METHODBUILDER;FEATURE_PDB_GENERATOR</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj b/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
index f729567c87c..1943a1f69ac 100644
--- a/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
+++ b/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj b/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
index d1c3506c85a..73b11b1c9a3 100644
--- a/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
+++ b/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj b/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj
index 847c7c0710f..94751b17b3f 100644
--- a/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj
+++ b/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_STRICT;MONO_DEPLOY</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_STRICT;MONO_DEPLOY</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_STRICT;MONO_DEPLOY</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_STRICT;MONO_DEPLOY</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj b/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
index 49de690c84e..be71f4029f2 100644
--- a/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
+++ b/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj b/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
index 8e07cc79a04..c7b9f5cfec7 100644
--- a/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
+++ b/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj b/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj
index 5cfd43427b7..74d98ad472c 100644
--- a/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj
+++ b/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Data/System.Data-net_4_x.csproj b/mcs/class/System.Data/System.Data-net_4_x.csproj
index b50eb0df32b..9608efe94c3 100644
--- a/mcs/class/System.Data/System.Data-net_4_x.csproj
+++ b/mcs/class/System.Data/System.Data-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,219,414,649</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;COREFX;PLATFORM_UNIX;USEOFFSET;MONO_PARTIAL_DATA_IMPORT</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;COREFX;PLATFORM_UNIX;USEOFFSET;MONO_PARTIAL_DATA_IMPORT</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,219,414,649</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;COREFX;PLATFORM_UNIX;USEOFFSET;MONO_PARTIAL_DATA_IMPORT</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;COREFX;PLATFORM_UNIX;USEOFFSET;MONO_PARTIAL_DATA_IMPORT</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj b/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
index 59c0761af5d..27250cd0518 100644
--- a/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
+++ b/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Design/System.Design-net_4_x.csproj b/mcs/class/System.Design/System.Design-net_4_x.csproj
index d9044aa61e5..0de9fd39ace 100644
--- a/mcs/class/System.Design/System.Design-net_4_x.csproj
+++ b/mcs/class/System.Design/System.Design-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj b/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
index adf6d2b4433..69aff5d5b04 100644
--- a/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
+++ b/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj b/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
index 3d6866bdd0f..14e4e0ab705 100644
--- a/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
+++ b/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj b/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj
index 871ef486040..03b19beb414 100644
--- a/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj
+++ b/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj b/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
index 1265cde832c..c6d6f6d86bc 100644
--- a/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
+++ b/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj b/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
index 7da381ce341..e750c1dfc78 100644
--- a/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
+++ b/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_TYPECONVERTER;SUPPORTS_WINDOWS_COLORS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_TYPECONVERTER;SUPPORTS_WINDOWS_COLORS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_TYPECONVERTER;SUPPORTS_WINDOWS_COLORS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_TYPECONVERTER;SUPPORTS_WINDOWS_COLORS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj b/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
index cb513a57929..30b51caf96a 100644
--- a/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
+++ b/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414,169</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CODEPLEX_40</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CODEPLEX_40</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414,169</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CODEPLEX_40</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CODEPLEX_40</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj b/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
index cb5643831a3..cc000d15eab 100644
--- a/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
+++ b/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,168,162</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,168,162</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj b/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
index 6284fdc8985..e7ce5a56ebe 100644
--- a/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
+++ b/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj b/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
index 6e237582de6..2219cf53924 100644
--- a/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
+++ b/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj b/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
index 1c682c481e5..646758f1aae 100644
--- a/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
+++ b/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj b/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
index dda6638bef0..219c266c6f8 100644
--- a/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
+++ b/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj b/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
index 60b9cca46fa..65ce1e5d029 100644
--- a/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
+++ b/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC;FEATURE_DYNAMIC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC;FEATURE_DYNAMIC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC;FEATURE_DYNAMIC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC;FEATURE_DYNAMIC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Json/System.Json-net_4_x.csproj b/mcs/class/System.Json/System.Json-net_4_x.csproj
index 54a854ba588..4f0fde6ab43 100644
--- a/mcs/class/System.Json/System.Json-net_4_x.csproj
+++ b/mcs/class/System.Json/System.Json-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Management/System.Management-net_4_x.csproj b/mcs/class/System.Management/System.Management-net_4_x.csproj
index 90589795802..4209191194a 100644
--- a/mcs/class/System.Management/System.Management-net_4_x.csproj
+++ b/mcs/class/System.Management/System.Management-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj b/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
index 83c46cdfba4..a10e83ba72a 100644
--- a/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
+++ b/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj b/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
index 874b6cdb9a5..af0c2089a05 100644
--- a/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
+++ b/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj b/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
index 5eecc426aee..9d65fd28560 100644
--- a/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
+++ b/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj b/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
index 7cc5093a2f6..cf0f31fc6cf 100644
--- a/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
+++ b/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Net/System.Net-net_4_x.csproj b/mcs/class/System.Net/System.Net-net_4_x.csproj
index 54584a85b15..3162032a761 100644
--- a/mcs/class/System.Net/System.Net-net_4_x.csproj
+++ b/mcs/class/System.Net/System.Net-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1720</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1720</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj b/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
index 1466512e844..1198c3316b2 100644
--- a/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
+++ b/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj b/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
index 9e8451461ed..89106fd4b4d 100644
--- a/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
+++ b/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj b/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
index cfcd654a6d7..e95d63072f6 100644
--- a/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj b/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
index b97766e4f07..fd612e3203d 100644
--- a/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj b/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
index 084806bf4b5..cb6c001fd6f 100644
--- a/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj b/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
index c7bdb9d4230..693b84ac424 100644
--- a/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj b/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
index 2d4a94460da..8b6aae1a2ee 100644
--- a/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj b/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
index 83469c2b7a5..3a6703d4a42 100644
--- a/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj b/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
index 13477dcb58b..d8bd9039d52 100644
--- a/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
+++ b/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj b/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
index e1692a166ab..88257ba6d89 100644
--- a/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj b/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
index f67fcef1759..51a3b170ba4 100644
--- a/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj b/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
index 06a2d2ea8de..a7a8f50d38c 100644
--- a/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj b/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
index 76cd2b76658..2f785634bec 100644
--- a/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;HAS_EDI;PREFERASYNC;PREFER_ASYNC;HAS_AWAIT;SIGNED</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj b/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
index 7a38a4d4d76..7bf9e27a412 100644
--- a/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
+++ b/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj b/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
index 66d36bd4d78..b079d06ac87 100644
--- a/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj b/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
index 74a75d64d9c..5776a725172 100644
--- a/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
+++ b/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.InteropServices.RuntimeInformation/System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj b/mcs/class/System.Runtime.InteropServices.RuntimeInformation/System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
index 81c6c0abbc3..59f32d42aa0 100644
--- a/mcs/class/System.Runtime.InteropServices.RuntimeInformation/System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
+++ b/mcs/class/System.Runtime.InteropServices.RuntimeInformation/System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj b/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
index 88e69b97155..cdc14c8471b 100644
--- a/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj b/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
index ed2007f92d1..dd4a5adca6d 100644
--- a/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj b/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
index c3a02fe2216..ed90c6f2011 100644
--- a/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,168,169,219,414,618,1634</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NO_DYNAMIC_CODEGEN;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NO_DYNAMIC_CODEGEN;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,168,169,219,414,618,1634</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NO_DYNAMIC_CODEGEN;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NO_DYNAMIC_CODEGEN;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Security/System.Security-net_4_x.csproj b/mcs/class/System.Security/System.Security-net_4_x.csproj
index ab9f2401ef1..89246bb50e0 100644
--- a/mcs/class/System.Security/System.Security-net_4_x.csproj
+++ b/mcs/class/System.Security/System.Security-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618,414</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SECURITY_DEP</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SECURITY_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618,414</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SECURITY_DEP</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SECURITY_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj b/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
index bdd50c9cbbd..b3dfd05ea61 100644
--- a/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
index 1f2ddc33a3e..00061969b87 100644
--- a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj b/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
index ffb6f6a5a66..32a1e26f61f 100644
--- a/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_FEATURE_MULTIPLE_APPDOMAINS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_FEATURE_MULTIPLE_APPDOMAINS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_FEATURE_MULTIPLE_APPDOMAINS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_FEATURE_MULTIPLE_APPDOMAINS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj b/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
index 8cdd5ff62e9..2baa6220515 100644
--- a/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj b/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
index fd43cf25870..3587a117577 100644
--- a/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj b/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
index 5dfbbb2d15a..82fe78cc270 100644
--- a/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;TRACE;NET_3_0;HAS_ACTIVATION</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;TRACE;NET_3_0;HAS_ACTIVATION</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;TRACE;NET_3_0;HAS_ACTIVATION</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;TRACE;NET_3_0;HAS_ACTIVATION</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj b/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
index 3f7b36f893e..de082d1fa2b 100644
--- a/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;TRACE;NET_3_0</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;TRACE;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;TRACE;NET_3_0</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;TRACE;NET_3_0</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj b/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
index dae6c57a828..7e945b62a50 100644
--- a/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
+++ b/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj b/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
index 7fe9af448ea..7149f98abb7 100644
--- a/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
+++ b/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONCURRENT_COLLECTIONS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONCURRENT_COLLECTIONS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONCURRENT_COLLECTIONS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONCURRENT_COLLECTIONS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj b/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
index cf59497a032..029beb3bf1a 100644
--- a/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
+++ b/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj b/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
index 8ed267f852a..c2148c4f6f2 100644
--- a/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
+++ b/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj b/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
index 5c972bb6251..44b914e312f 100644
--- a/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
+++ b/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SYSTEM_WEB_APPLICATIONSERVICES</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SYSTEM_WEB_APPLICATIONSERVICES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;SYSTEM_WEB_APPLICATIONSERVICES</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;SYSTEM_WEB_APPLICATIONSERVICES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj b/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
index fa53fad0c78..cf2d626ebc4 100644
--- a/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
+++ b/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj b/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
index 654e98a98a3..4589328cb73 100644
--- a/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
+++ b/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj b/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
index daba3d64b72..555b4e19cf4 100644
--- a/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
+++ b/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;SYSTEM_WEB_EXTENSIONS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;SYSTEM_WEB_EXTENSIONS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5;SYSTEM_WEB_EXTENSIONS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5;SYSTEM_WEB_EXTENSIONS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj b/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
index 6f65af38a6f..962e7fba1f7 100644
--- a/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
+++ b/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj b/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
index 010b0e9554a..0fa458435f5 100644
--- a/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
+++ b/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj b/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
index 1fb78e34822..6de49e3aa74 100644
--- a/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
+++ b/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETMVC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETMVC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj b/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
index dfd68de60bf..c0c1dc21961 100644
--- a/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
+++ b/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj b/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
index 43c71407757..92b91480a4a 100644
--- a/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
+++ b/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj b/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
index 78ad9a46337..93c6e8b2e40 100644
--- a/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
+++ b/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj b/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
index 8547ca3fe3e..bea58b03c2a 100644
--- a/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
+++ b/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj b/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
index 6c36eb0aa98..2d395564044 100644
--- a/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
+++ b/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj b/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
index ca1abc7d357..344eb6d7133 100644
--- a/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
+++ b/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,168,612,618,649</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_BROKEN_CONFIGURATION_DLL</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_BROKEN_CONFIGURATION_DLL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,168,612,618,649</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MONO_BROKEN_CONFIGURATION_DLL</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;MONO_BROKEN_CONFIGURATION_DLL</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj b/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
index 4ce8f2bcc47..74b69c57aae 100644
--- a/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj b/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
index 6a874017c52..c1a3b7a0cd4 100644
--- a/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj b/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
index b52a1332b95..4b43437324e 100644
--- a/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASPNETWEBPAGES</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASPNETWEBPAGES</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web/System.Web-net_4_x.csproj b/mcs/class/System.Web/System.Web-net_4_x.csproj
index 7732be367a3..0efc934033f 100644
--- a/mcs/class/System.Web/System.Web-net_4_x.csproj
+++ b/mcs/class/System.Web/System.Web-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,612,618,436,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_SYSTEM_WEB;WEBSERVICES_DEP</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_SYSTEM_WEB;WEBSERVICES_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,612,618,436,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_SYSTEM_WEB;WEBSERVICES_DEP</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_SYSTEM_WEB;WEBSERVICES_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj b/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
index 8ece36e1643..9ea6a6d579e 100644
--- a/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
+++ b/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,612,618,436,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_SYSTEM_WEB</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_SYSTEM_WEB</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,612,618,436,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;INSIDE_SYSTEM_WEB</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;INSIDE_SYSTEM_WEB</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj b/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
index cfe9c610ef9..9a2761e811a 100644
--- a/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
+++ b/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,67</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,67</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj b/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
index 8bbc300a64a..8d1f124a209 100644
--- a/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
+++ b/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,618,612,809</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,618,612,809</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Windows/System.Windows-net_4_x.csproj b/mcs/class/System.Windows/System.Windows-net_4_x.csproj
index 0c5e46b3ca6..d3b04065e71 100644
--- a/mcs/class/System.Windows/System.Windows-net_4_x.csproj
+++ b/mcs/class/System.Windows/System.Windows-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj b/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
index 0a46184494f..790bcbe4a09 100644
--- a/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
+++ b/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj b/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
index f916981d0ea..bf303db3ef5 100644
--- a/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
+++ b/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj b/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
index a10ccb568bb..ecc922b8f4e 100644
--- a/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
+++ b/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
@@ -35,7 +35,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -43,7 +43,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj b/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
index 5244d466702..c6fa9f18a70 100644
--- a/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
+++ b/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASYNC</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASYNC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASYNC</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASYNC</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.XML/System.Xml-net_4_x.csproj b/mcs/class/System.XML/System.Xml-net_4_x.csproj
index 14c2c3312d5..5c6128902ed 100644
--- a/mcs/class/System.XML/System.Xml-net_4_x.csproj
+++ b/mcs/class/System.XML/System.Xml-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASYNC;CONFIGURATION_DEP</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASYNC;CONFIGURATION_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;ASYNC;CONFIGURATION_DEP</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;ASYNC;CONFIGURATION_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj b/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
index 03232bbf567..6a975319b83 100644
--- a/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
+++ b/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj b/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
index 773813ccd4a..b90582957b9 100644
--- a/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
+++ b/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_SERIALIZATION</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_SERIALIZATION</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_SERIALIZATION</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_SERIALIZATION</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj b/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
index 27bfc2b0f5f..c834555074a 100644
--- a/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
+++ b/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System/System-bare-net_4_x.csproj b/mcs/class/System/System-bare-net_4_x.csproj
index f6c98cf17ea..ddb69a2c71a 100644
--- a/mcs/class/System/System-bare-net_4_x.csproj
+++ b/mcs/class/System/System-bare-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System/System-net_4_x.csproj b/mcs/class/System/System-net_4_x.csproj
index bf204056889..b80027dbb99 100644
--- a/mcs/class/System/System-net_4_x.csproj
+++ b/mcs/class/System/System-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS;CONFIGURATION_DEP</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS;CONFIGURATION_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS;CONFIGURATION_DEP</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS;CONFIGURATION_DEP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/System/System-secxml-net_4_x.csproj b/mcs/class/System/System-secxml-net_4_x.csproj
index 8b3a733f8c6..2a2b650b7a9 100644
--- a/mcs/class/System/System-secxml-net_4_x.csproj
+++ b/mcs/class/System/System-secxml-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,436</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;CONFIGURATION_2_0;FEATURE_PAL;SYSTEM_NAMESPACE;MONO;PLATFORM_UNIX;MONO_FEATURE_PROCESS_START;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;CODEDOM;MONO_FEATURE_APPLETLS;MONO_FEATURE_BTLS;SECURITY_DEP;XML_DEP;MONO_SECURITY_ALIAS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj b/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
index 4d3e62d85e6..d695de325c4 100644
--- a/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
+++ b/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj b/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
index feef07a2979..137ce52a0fb 100644
--- a/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
+++ b/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj b/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
index c773ee0edad..640a0a8d9d6 100644
--- a/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
+++ b/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,67,618</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,67,618</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/class/corlib/corlib-net_4_x.csproj b/mcs/class/corlib/corlib-net_4_x.csproj
index 2a38db0914b..11c56bde1f0 100644
--- a/mcs/class/corlib/corlib-net_4_x.csproj
+++ b/mcs/class/corlib/corlib-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>612,618,1635,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
+    <DefineConstants>TRACE;INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>612,618,1635,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
+    <DefineConstants>INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -846,6 +846,7 @@
     <Compile Include="corert\Interop.MemAllocFree.cs" />
     <Compile Include="corert\RelocatedTypeAttribute.cs" />
     <Compile Include="corert\RuntimeThread.cs" />
+    <Compile Include="corert\ThreadPoolBoundHandle.cs" />
     <Compile Include="Microsoft.Win32\IRegistryApi.cs" />
     <Compile Include="Microsoft.Win32\Registry.cs" />
     <Compile Include="Microsoft.Win32\RegistryHive.cs" />
diff --git a/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj b/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
index 1164355a18c..381656bb80f 100644
--- a/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
+++ b/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_3_5</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_3_5</DefineConstants>
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diff --git a/mcs/class/monodoc/monodoc-net_4_x.csproj b/mcs/class/monodoc/monodoc-net_4_x.csproj
index 12a4466000e..93dce300235 100644
--- a/mcs/class/monodoc/monodoc-net_4_x.csproj
+++ b/mcs/class/monodoc/monodoc-net_4_x.csproj
@@ -29,7 +29,7 @@
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-    <DefineConstants>TRACE;LEGACY_MODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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@@ -37,7 +37,7 @@
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-    <DefineConstants>LEGACY_MODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/ilasm/ilasm-net_4_x.csproj b/mcs/ilasm/ilasm-net_4_x.csproj
index 754e244dd0b..21ccffc3f0d 100644
--- a/mcs/ilasm/ilasm-net_4_x.csproj
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@@ -29,7 +29,7 @@
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-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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@@ -37,7 +37,7 @@
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     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
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diff --git a/mcs/mcs/mcs-net_4_x.csproj b/mcs/mcs/mcs-net_4_x.csproj
index 500633827a4..6b1f85fef5e 100644
--- a/mcs/mcs/mcs-net_4_x.csproj
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+    <DefineConstants>TRACE;STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_PROCESS_START;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
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@@ -37,7 +37,7 @@
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+    <DefineConstants>STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_PROCESS_START;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
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diff --git a/mcs/nunit24/ClientUtilities/util/nunit.util-net_4_x.csproj b/mcs/nunit24/ClientUtilities/util/nunit.util-net_4_x.csproj
index 63bdb02b357..bce06915e29 100644
--- a/mcs/nunit24/ClientUtilities/util/nunit.util-net_4_x.csproj
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-    <DefineConstants>TRACE;MONO;StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;MONO;StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
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@@ -42,7 +42,7 @@
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-    <DefineConstants>MONO;StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/nunit24/ConsoleRunner/nunit-console-exe/nunit-console-net_4_x.csproj b/mcs/nunit24/ConsoleRunner/nunit-console-exe/nunit-console-net_4_x.csproj
index 2d481a2a57a..2cf28af5be3 100644
--- a/mcs/nunit24/ConsoleRunner/nunit-console-exe/nunit-console-net_4_x.csproj
+++ b/mcs/nunit24/ConsoleRunner/nunit-console-exe/nunit-console-net_4_x.csproj
@@ -29,7 +29,7 @@
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-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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@@ -37,7 +37,7 @@
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-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/nunit24/ConsoleRunner/nunit-console/nunit-console-runner-net_4_x.csproj b/mcs/nunit24/ConsoleRunner/nunit-console/nunit-console-runner-net_4_x.csproj
index a222b28a0ac..37435c81963 100644
--- a/mcs/nunit24/ConsoleRunner/nunit-console/nunit-console-runner-net_4_x.csproj
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@@ -34,7 +34,7 @@
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@@ -42,7 +42,7 @@
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-    <DefineConstants>MONO;StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/nunit24/NUnitCore/core/nunit.core-net_4_x.csproj b/mcs/nunit24/NUnitCore/core/nunit.core-net_4_x.csproj
index 8ec4b0fd284..75170c0d56a 100644
--- a/mcs/nunit24/NUnitCore/core/nunit.core-net_4_x.csproj
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@@ -42,7 +42,7 @@
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-    <DefineConstants>StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/nunit24/NUnitCore/interfaces/nunit.core.interfaces-net_4_x.csproj b/mcs/nunit24/NUnitCore/interfaces/nunit.core.interfaces-net_4_x.csproj
index 39be7828f20..50ad2aa20d3 100644
--- a/mcs/nunit24/NUnitCore/interfaces/nunit.core.interfaces-net_4_x.csproj
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@@ -42,7 +42,7 @@
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-    <DefineConstants>StronglyNamedAssembly;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
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diff --git a/mcs/nunit24/NUnitExtensions/core/nunit.core.extensions-net_4_x.csproj b/mcs/nunit24/NUnitExtensions/core/nunit.core.extensions-net_4_x.csproj
index 580846d4bbc..064a51bbec7 100644
--- a/mcs/nunit24/NUnitExtensions/core/nunit.core.extensions-net_4_x.csproj
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@@ -34,7 +34,7 @@
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@@ -42,7 +42,7 @@
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diff --git a/mcs/nunit24/NUnitExtensions/framework/nunit.framework.extensions-net_4_x.csproj b/mcs/nunit24/NUnitExtensions/framework/nunit.framework.extensions-net_4_x.csproj
index 7c471cec0a0..a16431c6336 100644
--- a/mcs/nunit24/NUnitExtensions/framework/nunit.framework.extensions-net_4_x.csproj
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@@ -42,7 +42,7 @@
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diff --git a/mcs/nunit24/NUnitFramework/framework/NUnit.Framework-net_4_x.csproj b/mcs/nunit24/NUnitFramework/framework/NUnit.Framework-net_4_x.csproj
index 9e6a5a7395f..215ee339729 100644
--- a/mcs/nunit24/NUnitFramework/framework/NUnit.Framework-net_4_x.csproj
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@@ -42,7 +42,7 @@
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diff --git a/mcs/nunit24/NUnitMocks/mocks/nunit.mocks-net_4_x.csproj b/mcs/nunit24/NUnitMocks/mocks/nunit.mocks-net_4_x.csproj
index c22ca7daabe..6f0fe6532c0 100644
--- a/mcs/nunit24/NUnitMocks/mocks/nunit.mocks-net_4_x.csproj
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@@ -42,7 +42,7 @@
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diff --git a/mcs/tools/al/al-net_4_x.csproj b/mcs/tools/al/al-net_4_x.csproj
index d79c6c554fd..b9980412f64 100644
--- a/mcs/tools/al/al-net_4_x.csproj
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@@ -37,7 +37,7 @@
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diff --git a/mcs/tools/browsercaps-updater/browsercaps-updater-net_4_x.csproj b/mcs/tools/browsercaps-updater/browsercaps-updater-net_4_x.csproj
index 9018ca5f22d..2d5dc903916 100644
--- a/mcs/tools/browsercaps-updater/browsercaps-updater-net_4_x.csproj
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@@ -37,7 +37,7 @@
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diff --git a/mcs/tools/cccheck/cccheck-net_4_x.csproj b/mcs/tools/cccheck/cccheck-net_4_x.csproj
index 0a23cc416cb..82037fe8104 100644
--- a/mcs/tools/cccheck/cccheck-net_4_x.csproj
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@@ -37,7 +37,7 @@
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diff --git a/mcs/tools/ccrewrite/ccrewrite-net_4_x.csproj b/mcs/tools/ccrewrite/ccrewrite-net_4_x.csproj
index 84ae9b88cb5..9f74786c7ed 100644
--- a/mcs/tools/ccrewrite/ccrewrite-net_4_x.csproj
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@@ -37,7 +37,7 @@
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diff --git a/mcs/tools/cil-stringreplacer/cil-stringreplacer-net_4_x.csproj b/mcs/tools/cil-stringreplacer/cil-stringreplacer-net_4_x.csproj
index c65542683e2..9265e632aeb 100644
--- a/mcs/tools/cil-stringreplacer/cil-stringreplacer-net_4_x.csproj
+++ b/mcs/tools/cil-stringreplacer/cil-stringreplacer-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/cil-strip/mono-cil-strip-net_4_x.csproj b/mcs/tools/cil-strip/mono-cil-strip-net_4_x.csproj
index 95ae82184b8..3fe5ff8bda7 100644
--- a/mcs/tools/cil-strip/mono-cil-strip-net_4_x.csproj
+++ b/mcs/tools/cil-strip/mono-cil-strip-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/commoncryptogenerator/commoncryptogenerator-net_4_x.csproj b/mcs/tools/commoncryptogenerator/commoncryptogenerator-net_4_x.csproj
index a91cd22633b..7dc46c86147 100644
--- a/mcs/tools/commoncryptogenerator/commoncryptogenerator-net_4_x.csproj
+++ b/mcs/tools/commoncryptogenerator/commoncryptogenerator-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/compiler-tester/compiler-tester-net_4_x.csproj b/mcs/tools/compiler-tester/compiler-tester-net_4_x.csproj
index d7c2daf16af..f1f1c763f26 100644
--- a/mcs/tools/compiler-tester/compiler-tester-net_4_x.csproj
+++ b/mcs/tools/compiler-tester/compiler-tester-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/corcompare/mono-api-info-net_4_x.csproj b/mcs/tools/corcompare/mono-api-info-net_4_x.csproj
index 29918a47398..bbbcb901100 100644
--- a/mcs/tools/corcompare/mono-api-info-net_4_x.csproj
+++ b/mcs/tools/corcompare/mono-api-info-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/csharp/csharp-net_4_x.csproj b/mcs/tools/csharp/csharp-net_4_x.csproj
index 1be6b4dd16e..5b367264648 100644
--- a/mcs/tools/csharp/csharp-net_4_x.csproj
+++ b/mcs/tools/csharp/csharp-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>3021,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>3021,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/culevel/culevel-net_4_x.csproj b/mcs/tools/culevel/culevel-net_4_x.csproj
index b9e7adc3e75..956e9b7a3f4 100644
--- a/mcs/tools/culevel/culevel-net_4_x.csproj
+++ b/mcs/tools/culevel/culevel-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/disco/disco-net_4_x.csproj b/mcs/tools/disco/disco-net_4_x.csproj
index 379e8001f0c..226b4b2670e 100644
--- a/mcs/tools/disco/disco-net_4_x.csproj
+++ b/mcs/tools/disco/disco-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/dtd2rng/dtd2rng-net_4_x.csproj b/mcs/tools/dtd2rng/dtd2rng-net_4_x.csproj
index 3dcca34130a..721bb4e18c6 100644
--- a/mcs/tools/dtd2rng/dtd2rng-net_4_x.csproj
+++ b/mcs/tools/dtd2rng/dtd2rng-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/dtd2xsd/dtd2xsd-net_4_x.csproj b/mcs/tools/dtd2xsd/dtd2xsd-net_4_x.csproj
index 99f766d8b6b..987b3e08c0b 100644
--- a/mcs/tools/dtd2xsd/dtd2xsd-net_4_x.csproj
+++ b/mcs/tools/dtd2xsd/dtd2xsd-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/gacutil/gacutil-net_4_x.csproj b/mcs/tools/gacutil/gacutil-net_4_x.csproj
index 2343a176d71..e28903b2d25 100644
--- a/mcs/tools/gacutil/gacutil-net_4_x.csproj
+++ b/mcs/tools/gacutil/gacutil-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/genxs/genxs-net_4_x.csproj b/mcs/tools/genxs/genxs-net_4_x.csproj
index 97425266a12..c374db323a5 100644
--- a/mcs/tools/genxs/genxs-net_4_x.csproj
+++ b/mcs/tools/genxs/genxs-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/ictool/ictool-net_4_x.csproj b/mcs/tools/ictool/ictool-net_4_x.csproj
index fece88935d6..3ea7b938e93 100644
--- a/mcs/tools/ictool/ictool-net_4_x.csproj
+++ b/mcs/tools/ictool/ictool-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/ikdasm/ikdasm-net_4_x.csproj b/mcs/tools/ikdasm/ikdasm-net_4_x.csproj
index 4708bb99e3e..bca5f17109d 100644
--- a/mcs/tools/ikdasm/ikdasm-net_4_x.csproj
+++ b/mcs/tools/ikdasm/ikdasm-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/installutil/installutil-net_4_x.csproj b/mcs/tools/installutil/installutil-net_4_x.csproj
index 352cc11d56b..6d91f7cd9a0 100644
--- a/mcs/tools/installutil/installutil-net_4_x.csproj
+++ b/mcs/tools/installutil/installutil-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/installvst/installvst-net_4_x.csproj b/mcs/tools/installvst/installvst-net_4_x.csproj
index b6fd6b5bd71..6e8c8846c90 100644
--- a/mcs/tools/installvst/installvst-net_4_x.csproj
+++ b/mcs/tools/installvst/installvst-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/lc/lc-net_4_x.csproj b/mcs/tools/lc/lc-net_4_x.csproj
index 356e6421ce7..c538fc60339 100644
--- a/mcs/tools/lc/lc-net_4_x.csproj
+++ b/mcs/tools/lc/lc-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/linker-analyzer/linkeranalyzer-net_4_x.csproj b/mcs/tools/linker-analyzer/linkeranalyzer-net_4_x.csproj
index 4adbf2b6e2d..c787b49456d 100644
--- a/mcs/tools/linker-analyzer/linkeranalyzer-net_4_x.csproj
+++ b/mcs/tools/linker-analyzer/linkeranalyzer-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/linker/monolinker-net_4_x.csproj b/mcs/tools/linker/monolinker-net_4_x.csproj
index 13dc651863c..b4aab447f35 100644
--- a/mcs/tools/linker/monolinker-net_4_x.csproj
+++ b/mcs/tools/linker/monolinker-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/macpack/macpack-net_4_x.csproj b/mcs/tools/macpack/macpack-net_4_x.csproj
index c0ecaccc639..0f47be1811c 100644
--- a/mcs/tools/macpack/macpack-net_4_x.csproj
+++ b/mcs/tools/macpack/macpack-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mconfig/mconfig-net_4_x.csproj b/mcs/tools/mconfig/mconfig-net_4_x.csproj
index d465b4450ce..d105b12992a 100644
--- a/mcs/tools/mconfig/mconfig-net_4_x.csproj
+++ b/mcs/tools/mconfig/mconfig-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mdb2ppdb/mdb2ppdb-net_4_x.csproj b/mcs/tools/mdb2ppdb/mdb2ppdb-net_4_x.csproj
index 19a93b9c4f9..76eeb47c017 100644
--- a/mcs/tools/mdb2ppdb/mdb2ppdb-net_4_x.csproj
+++ b/mcs/tools/mdb2ppdb/mdb2ppdb-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mdbrebase/mdbrebase-net_4_x.csproj b/mcs/tools/mdbrebase/mdbrebase-net_4_x.csproj
index 7ca9baff063..348bfe91fef 100644
--- a/mcs/tools/mdbrebase/mdbrebase-net_4_x.csproj
+++ b/mcs/tools/mdbrebase/mdbrebase-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mdoc/mdoc-net_4_x.csproj b/mcs/tools/mdoc/mdoc-net_4_x.csproj
index 944e0bcc710..dac15a6d977 100644
--- a/mcs/tools/mdoc/mdoc-net_4_x.csproj
+++ b/mcs/tools/mdoc/mdoc-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mkbundle/mkbundle-net_4_x.csproj b/mcs/tools/mkbundle/mkbundle-net_4_x.csproj
index 67472975378..80433bbaf6e 100644
--- a/mcs/tools/mkbundle/mkbundle-net_4_x.csproj
+++ b/mcs/tools/mkbundle/mkbundle-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>STATIC;NO_SYMBOL_WRITER;NO_AUTHENTICODE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mod/mod-net_4_x.csproj b/mcs/tools/mod/mod-net_4_x.csproj
index c97177b9def..6cfe10808f8 100644
--- a/mcs/tools/mod/mod-net_4_x.csproj
+++ b/mcs/tools/mod/mod-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-api-html/mono-api-html-net_4_x.csproj b/mcs/tools/mono-api-html/mono-api-html-net_4_x.csproj
index 0f0b92693ba..7aa34e8faff 100644
--- a/mcs/tools/mono-api-html/mono-api-html-net_4_x.csproj
+++ b/mcs/tools/mono-api-html/mono-api-html-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-configuration-crypto/cli/mono-configuration-crypto-net_4_x.csproj b/mcs/tools/mono-configuration-crypto/cli/mono-configuration-crypto-net_4_x.csproj
index 11a3bab7f41..4900dfc2c40 100644
--- a/mcs/tools/mono-configuration-crypto/cli/mono-configuration-crypto-net_4_x.csproj
+++ b/mcs/tools/mono-configuration-crypto/cli/mono-configuration-crypto-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-configuration-crypto/lib/Mono.Configuration.Crypto-net_4_x.csproj b/mcs/tools/mono-configuration-crypto/lib/Mono.Configuration.Crypto-net_4_x.csproj
index 98555d0c674..9694cfdeabf 100644
--- a/mcs/tools/mono-configuration-crypto/lib/Mono.Configuration.Crypto-net_4_x.csproj
+++ b/mcs/tools/mono-configuration-crypto/lib/Mono.Configuration.Crypto-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-service/mono-service-net_4_x.csproj b/mcs/tools/mono-service/mono-service-net_4_x.csproj
index baca85de2af..0e49107295b 100644
--- a/mcs/tools/mono-service/mono-service-net_4_x.csproj
+++ b/mcs/tools/mono-service/mono-service-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-shlib-cop/mono-shlib-cop-net_4_x.csproj b/mcs/tools/mono-shlib-cop/mono-shlib-cop-net_4_x.csproj
index 3b81f555618..d2e41439c10 100644
--- a/mcs/tools/mono-shlib-cop/mono-shlib-cop-net_4_x.csproj
+++ b/mcs/tools/mono-shlib-cop/mono-shlib-cop-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-symbolicate/mono-symbolicate-net_4_x.csproj b/mcs/tools/mono-symbolicate/mono-symbolicate-net_4_x.csproj
index 2e17b66e816..7be7adfdb06 100644
--- a/mcs/tools/mono-symbolicate/mono-symbolicate-net_4_x.csproj
+++ b/mcs/tools/mono-symbolicate/mono-symbolicate-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>649,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NO_AUTHENTICODE;CECIL;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NO_AUTHENTICODE;CECIL;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>649,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NO_AUTHENTICODE;CECIL;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NO_AUTHENTICODE;CECIL;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-xmltool/mono-xmltool-net_4_x.csproj b/mcs/tools/mono-xmltool/mono-xmltool-net_4_x.csproj
index 17add133e40..f5b18f9a3ea 100644
--- a/mcs/tools/mono-xmltool/mono-xmltool-net_4_x.csproj
+++ b/mcs/tools/mono-xmltool/mono-xmltool-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/mono-xsd/xsd-net_4_x.csproj b/mcs/tools/mono-xsd/xsd-net_4_x.csproj
index 86a2121d394..c7f898a1b2d 100644
--- a/mcs/tools/mono-xsd/xsd-net_4_x.csproj
+++ b/mcs/tools/mono-xsd/xsd-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/monop/monop-net_4_x.csproj b/mcs/tools/monop/monop-net_4_x.csproj
index 1368dcfdfb8..f1252b5cedb 100644
--- a/mcs/tools/monop/monop-net_4_x.csproj
+++ b/mcs/tools/monop/monop-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NO_AUTHENTICODE;STATIC;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NO_AUTHENTICODE;STATIC;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NO_AUTHENTICODE;STATIC;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NO_AUTHENTICODE;STATIC;NO_SYMBOL_WRITER;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/nunitreport/nunitreport-net_4_x.csproj b/mcs/tools/nunitreport/nunitreport-net_4_x.csproj
index a65042f2329..bf0cd3c8161 100644
--- a/mcs/tools/nunitreport/nunitreport-net_4_x.csproj
+++ b/mcs/tools/nunitreport/nunitreport-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/pdb2mdb/pdb2mdb-net_4_x.csproj b/mcs/tools/pdb2mdb/pdb2mdb-net_4_x.csproj
index 4ffaddf33b9..40067ab53c4 100644
--- a/mcs/tools/pdb2mdb/pdb2mdb-net_4_x.csproj
+++ b/mcs/tools/pdb2mdb/pdb2mdb-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/resgen/resgen-net_4_x.csproj b/mcs/tools/resgen/resgen-net_4_x.csproj
index ad6adbc9ca3..5231cecebc7 100644
--- a/mcs/tools/resgen/resgen-net_4_x.csproj
+++ b/mcs/tools/resgen/resgen-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699,1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/sgen/sgen-net_4_x.csproj b/mcs/tools/sgen/sgen-net_4_x.csproj
index 9eaf6d4a740..7708bdbba00 100644
--- a/mcs/tools/sgen/sgen-net_4_x.csproj
+++ b/mcs/tools/sgen/sgen-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/soapsuds/soapsuds-net_4_x.csproj b/mcs/tools/soapsuds/soapsuds-net_4_x.csproj
index 1f31cca4147..70a51ff7a46 100644
--- a/mcs/tools/soapsuds/soapsuds-net_4_x.csproj
+++ b/mcs/tools/soapsuds/soapsuds-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/sqlmetal/sqlmetal-net_4_x.csproj b/mcs/tools/sqlmetal/sqlmetal-net_4_x.csproj
index 63ad5a3c22a..81f55069f3d 100644
--- a/mcs/tools/sqlmetal/sqlmetal-net_4_x.csproj
+++ b/mcs/tools/sqlmetal/sqlmetal-net_4_x.csproj
@@ -34,7 +34,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;MONO_STRICT;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;MONO_STRICT;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -42,7 +42,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>MONO_STRICT;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>MONO_STRICT;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/sqlsharp/sqlsharp-net_4_x.csproj b/mcs/tools/sqlsharp/sqlsharp-net_4_x.csproj
index 43a8a65e640..e9bb6281922 100644
--- a/mcs/tools/sqlsharp/sqlsharp-net_4_x.csproj
+++ b/mcs/tools/sqlsharp/sqlsharp-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/svcutil/svcutil-net_4_x.csproj b/mcs/tools/svcutil/svcutil-net_4_x.csproj
index 8db3b78861f..fe457fc59a7 100644
--- a/mcs/tools/svcutil/svcutil-net_4_x.csproj
+++ b/mcs/tools/svcutil/svcutil-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/mcs/tools/wsdl/wsdl-net_4_x.csproj b/mcs/tools/wsdl/wsdl-net_4_x.csproj
index 824d2aa47f1..db100eec5e7 100644
--- a/mcs/tools/wsdl/wsdl-net_4_x.csproj
+++ b/mcs/tools/wsdl/wsdl-net_4_x.csproj
@@ -29,7 +29,7 @@
     <DebugType>full</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>false</Optimize>
-    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>TRACE;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -37,7 +37,7 @@
     <DebugType>pdbonly</DebugType>
     <NoWarn>1699</NoWarn>
     <Optimize>true</Optimize>
-    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM</DefineConstants>
+    <DefineConstants>NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>