[System] Clear MONO_CFG_DIR before starting mcs in CodeDOM CSharpCodeGenerator for XM4.5 (#13742)

* [System] Clear MONO_CFG_DIR before starting mcs in CodeDOM CSharpCodeGenerator

This showed up in the xamarin-macios 2019-02 integration.
When you used Xslt with a custom C# script in a Xamarin.Mac Full application
we'd try to launch mcs via CodeDOM to compile the script.

This started failing in 2019-02 because System.Native (mono-native) wasn't found,
the reason is that XM sets MONO_CFG_DIR to point to the Contents/MonoBundle
in the app bundle where it packages the global config file with dllmaps.

However the started Mono wasn't able to find mono-native since the config
there uses a different name for the file.

To prevent that we now clear MONO_CFG_DIR so it uses the default value for the
mono process we're starting (note that setting it to String.Empty doesn't work)

* Make it specific to XM 4.5

1 files changed, 9 insertions, 1 deletions

diff --git a/mcs/class/System/Microsoft.CSharp/CSharpCodeGenerator.cs b/mcs/class/System/Microsoft.CSharp/CSharpCodeGenerator.cs
index 9bb045dfab1..d877e05496d 100644
--- a/mcs/class/System/Microsoft.CSharp/CSharpCodeGenerator.cs
+++ b/mcs/class/System/Microsoft.CSharp/CSharpCodeGenerator.cs
@@ -90,7 +90,15 @@ namespace Microsoft.CSharp
 			 * reset MONO_GC_PARAMS - we are invoking compiler possibly with another GC that
 			 * may not handle some of the options causing compilation failure
 			 */
-			mcs.StartInfo.EnvironmentVariables ["MONO_GC_PARAMS"] = String.Empty;
+			mcs.StartInfo.EnvironmentVariables.Remove ("MONO_GC_PARAMS");
+
+#if XAMMAC_4_5
+			/*/
+			 * reset MONO_CFG_DIR - we don't want to propagate the current config to another mono
+			 * since it's specific to the XM application and won't work on system mono.
+			 */
+			mcs.StartInfo.EnvironmentVariables.Remove ("MONO_CFG_DIR");
+#endif
 
 			mcs.StartInfo.CreateNoWindow=true;
 			mcs.StartInfo.UseShellExecute=false;