Windows: Add support for building with clang.

This commit contains the minimum to make clang build/work with blender, asan and ninja build support is forthcoming

Things to note:

1) Builds and runs, and is able to pass all tests (except for the freestyle_stroke_material.blend test which was broken at that time for all platforms by the looks of it)

2) It's slightly faster than msvc when using cycles. (time in seconds, on an i7-3370)

victor_cpu
	msvc:3099.51
	clang:2796.43

pavillon_barcelona_cpu
	msvc:1872.05
	clang:1827.72

koro_cpu
	msvc:1097.58
	clang:1006.51

fishy_cat_cpu
	msvc:815.37
	clang:722.2

classroom_cpu
	msvc:1705.39
	clang:1575.43

bmw27_cpu
	msvc:552.38
	clang:561.53

barbershop_interior_cpu
	msvc:2134.93
	clang:1922.33

3) clang on windows uses a drop in replacement for the Microsoft cl.exe (takes some of the Microsoft parameters, but not all, and takes some of the clang parameters but not all) and uses ms headers + libraries + linker, so you still need visual studio installed and will use our existing vc14 svn libs.

4) X64 only currently, X86 builds but crashes on startup.

5) Tested with llvm/clang 6.0.0

6) Requires visual studio integration, available at https://github.com/LazyDodo/llvm-vs2017-integration

7) The Microsoft compiler spawns a few copies of cl in parallel to get faster build times, clang doesn't, so the build time is 3-4x slower than with msvc.

8) No openmp support yet. Have not looked at this much, the binary distribution of clang doesn't seem to include it on windows.

9) No ASAN support yet, some of the sanitizers can be made to work, but it was decided to leave support out of this commit.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D3304

7 files changed, 76 insertions, 3 deletions

diff --git a/build_files/build_environment/patches/boost.diff b/build_files/build_environment/patches/boost.diff
index ea3ec035518..41b40d7a915 100644
--- a/build_files/build_environment/patches/boost.diff
+++ b/build_files/build_environment/patches/boost.diff
@@ -13,3 +13,25 @@
 -#     pragma message("Unknown compiler version - please run the configure tests and report the results")
 -#  endif
 -#endif
+--- a/boost/type_traits/has_nothrow_assign.hpp	2015-12-13 05:49:42 -0700
++++ b/boost/type_traits/has_nothrow_assign.hpp	2018-05-27 11:11:02 -0600
+@@ -24,7 +24,7 @@
+ #include <boost/type_traits/remove_reference.hpp>
+ #endif
+ #endif
+-#if defined(__GNUC__) || defined(__SUNPRO_CC)
++#if defined(__GNUC__) || defined(__SUNPRO_CC) || defined(__clang__)
+ #include <boost/type_traits/is_const.hpp>
+ #include <boost/type_traits/is_volatile.hpp>
+ #include <boost/type_traits/is_assignable.hpp>
+--- a/boost/type_traits/has_nothrow_constructor.hpp	2015-12-13 05:49:42 -0700
++++ b/boost/type_traits/has_nothrow_constructor.hpp	2018-05-27 11:11:02 -0600
+@@ -17,7 +17,7 @@
+ #if defined(BOOST_MSVC) || defined(BOOST_INTEL)
+ #include <boost/type_traits/has_trivial_constructor.hpp>
+ #endif
+-#if defined(__GNUC__ ) || defined(__SUNPRO_CC)
++#if defined(__GNUC__ ) || defined(__SUNPRO_CC) || defined(__clang__)
+ #include <boost/type_traits/is_default_constructible.hpp>
+ #endif
+ 
diff --git a/build_files/build_environment/patches/osl.diff b/build_files/build_environment/patches/osl.diff
index fcb5ec4165f..960a2506374 100644
--- a/build_files/build_environment/patches/osl.diff
+++ b/build_files/build_environment/patches/osl.diff
@@ -10,3 +10,29 @@ diff -Naur osl/src/external_osl/src/cmake/flexbison.cmake osl_bak/src/external_o
            MAIN_DEPENDENCY ${flexsrc}
            DEPENDS ${${compiler_headers}}
            WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} )
+--- a/src/include/OSL/oslconfig.h	2016-10-31 16:48:19 -0600
++++ b/src/include/OSL/oslconfig.h	2018-05-27 11:18:08 -0600
+@@ -44,12 +44,18 @@
+ // same if another packages is compiling against OSL and using these headers
+ // (OSL may be C++11 but the client package may be older, or vice versa --
+ // use these two symbols to differentiate these cases, when important).
+-#if (__cplusplus >= 201402L)
+-#  define OSL_CPLUSPLUS_VERSION  14
+-#elif (__cplusplus >= 201103L)
+-#  define OSL_CPLUSPLUS_VERSION  11
++
++// Force C++03 for MSVC in blender since svn the libraries are build with that
++#if !defined(_MSC_VER)
++	#if (__cplusplus >= 201402L)
++	#  define OSL_CPLUSPLUS_VERSION  14
++	#elif (__cplusplus >= 201103L)
++	#  define OSL_CPLUSPLUS_VERSION  11
++	#else
++	#  define OSL_CPLUSPLUS_VERSION  3 /* presume C++03 */
++	#endif
+ #else
+-#  define OSL_CPLUSPLUS_VERSION  3 /* presume C++03 */
++	#  define OSL_CPLUSPLUS_VERSION  3 /* presume C++03 */
+ #endif
+ 
+ // Symbol export defines
diff --git a/build_files/cmake/platform/platform_win32.cmake b/build_files/cmake/platform/platform_win32.cmake
index 3520ac9c075..205040ac0cf 100644
--- a/build_files/cmake/platform/platform_win32.cmake
+++ b/build_files/cmake/platform/platform_win32.cmake
@@ -29,7 +29,10 @@ if(NOT MSVC)
 	message(FATAL_ERROR "Compiler is unsupported")
 endif()
 
-# Libraries configuration for Windows when compiling with MSVC.
+if(CMAKE_C_COMPILER_ID MATCHES "Clang")
+	set(MSVC_CLANG On)
+	file(TO_CMAKE_PATH $ENV{VCToolsRedistDir} MSVC_REDIST_DIR)
+endif()
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ${WINDOWS_USE_VISUAL_STUDIO_FOLDERS})
 
@@ -121,8 +124,16 @@ include(InstallRequiredSystemLibraries)
 
 remove_cc_flag("/MDd" "/MD")
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /nologo /J /Gd /MP /EHsc")
-set(CMAKE_C_FLAGS     "${CMAKE_C_FLAGS} /nologo /J /Gd /MP")
+if(MSVC_CLANG) # Clangs version of cl doesn't support all flags 
+	if(NOT WITH_CXX11) # C++11 is on by default in clang-cl and can't be turned off, if c++11 is not enabled in blender repress some c++11 related warnings. 
+		set(CXX_WARN_FLAGS "-Wno-inconsistent-missing-override")
+	endif()
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXX_WARN_FLAGS} /nologo /J /Gd /EHsc -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference ")
+	set(CMAKE_C_FLAGS     "${CMAKE_C_FLAGS} /nologo /J /Gd -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference")
+else()
+	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /nologo /J /Gd /MP /EHsc")
+	set(CMAKE_C_FLAGS     "${CMAKE_C_FLAGS} /nologo /J /Gd /MP")
+endif()
 
 set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} /MTd")
 set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} /MTd")
diff --git a/build_files/windows/configure_msbuild.cmd b/build_files/windows/configure_msbuild.cmd
index 135b7933ab2..95a8882a9ab 100644
--- a/build_files/windows/configure_msbuild.cmd
+++ b/build_files/windows/configure_msbuild.cmd
@@ -4,6 +4,10 @@ if "%BUILD_ARCH%"=="x64" (
 	set MSBUILD_PLATFORM=x64
 ) else if "%BUILD_ARCH%"=="x86" (
 	set MSBUILD_PLATFORM=win32
+	if "%WITH_CLANG%"=="1" (
+		echo Clang not supported for X86
+		exit /b 1
+	)
 )
 
 if NOT EXIST %BUILD_DIR%\nul (
diff --git a/build_files/windows/configure_ninja.cmd b/build_files/windows/configure_ninja.cmd
index 13797543bcc..24911a10275 100644
--- a/build_files/windows/configure_ninja.cmd
+++ b/build_files/windows/configure_ninja.cmd
@@ -1,4 +1,10 @@
 set BUILD_CMAKE_ARGS=%BUILD_CMAKE_ARGS% -G "Ninja" %TESTS_CMAKE_ARGS% -DCMAKE_BUILD_TYPE=%BUILD_TYPE%
+
+if "%WITH_CLANG%" == "1" (
+	echo Building with ninja and clang not supported yet.
+	exit /b 1
+)
+
 :DetectionComplete
 if NOT "%verbose%" == "" (
 	echo BUILD_CMAKE_ARGS=%BUILD_CMAKE_ARGS% 
diff --git a/build_files/windows/parse_arguments.cmd b/build_files/windows/parse_arguments.cmd
index 5a82bf3cf04..1cb2e1f3e8c 100644
--- a/build_files/windows/parse_arguments.cmd
+++ b/build_files/windows/parse_arguments.cmd
@@ -36,6 +36,9 @@ if NOT "%1" == "" (
 	) else if "%1" == "bpy" (
 		set TARGET=Bpy
 		set BUILD_CMAKE_ARGS=%BUILD_CMAKE_ARGS% -C"%BLENDER_DIR%\build_files\cmake\config\bpy_module.cmake"
+	) else if "%1" == "clang" (
+		set BUILD_CMAKE_ARGS=%BUILD_CMAKE_ARGS% -T"LLVM-vs2017"
+		set WITH_CLANG=1
 	) else if "%1" == "release" (
 		set TARGET=Release
 	) else if "%1" == "x86" (
diff --git a/build_files/windows/reset_variables.cmd b/build_files/windows/reset_variables.cmd
index 34af3ff9389..d9a50a7f809 100644
--- a/build_files/windows/reset_variables.cmd
+++ b/build_files/windows/reset_variables.cmd
@@ -21,3 +21,4 @@ set BUILD_UPDATE=
 set BUILD_SHOW_HASHES=
 set SHOW_HELP=
 set BUILD_WITH_NINJA=
+set WITH_CLANG=
\ No newline at end of file