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

5 files changed, 7 insertions, 7 deletions

diff --git a/source/blender/blenkernel/intern/rigidbody.c b/source/blender/blenkernel/intern/rigidbody.c
index b8873cca0fb..ecb8814dd70 100644
--- a/source/blender/blenkernel/intern/rigidbody.c
+++ b/source/blender/blenkernel/intern/rigidbody.c
@@ -1658,7 +1658,7 @@ void BKE_rigidbody_do_simulation(Scene *scene, float ctime)
 #else  /* WITH_BULLET */
 
 /* stubs */
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #  pragma GCC diagnostic push
 #  pragma GCC diagnostic ignored "-Wunused-parameter"
 #endif
@@ -1684,7 +1684,7 @@ void BKE_rigidbody_cache_reset(RigidBodyWorld *rbw) {}
 void BKE_rigidbody_rebuild_world(Scene *scene, float ctime) {}
 void BKE_rigidbody_do_simulation(Scene *scene, float ctime) {}
 
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #  pragma GCC diagnostic pop
 #endif
 
diff --git a/source/blender/blenlib/BLI_utildefines.h b/source/blender/blenlib/BLI_utildefines.h
index c0b76aa9cbf..75ddb5e739c 100644
--- a/source/blender/blenlib/BLI_utildefines.h
+++ b/source/blender/blenlib/BLI_utildefines.h
@@ -552,13 +552,13 @@ extern bool BLI_memory_is_zero(const void *arr, const size_t arr_size);
 
 
 /* UNUSED macro, for function argument */
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__) 
 #  define UNUSED(x) UNUSED_ ## x __attribute__((__unused__))
 #else
 #  define UNUSED(x) UNUSED_ ## x
 #endif
 
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__) 
 #  define UNUSED_FUNCTION(x) __attribute__((__unused__)) UNUSED_ ## x
 #else
 #  define UNUSED_FUNCTION(x) UNUSED_ ## x
diff --git a/source/blender/bmesh/CMakeLists.txt b/source/blender/bmesh/CMakeLists.txt
index 5245d24a075..320bebc9958 100644
--- a/source/blender/bmesh/CMakeLists.txt
+++ b/source/blender/bmesh/CMakeLists.txt
@@ -169,7 +169,7 @@ set(SRC
 	bmesh_tools.h
 )
 
-if(MSVC)
+if(MSVC AND NOT MSVC_CLANG)
 	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX /wd4101")
 endif()
 
diff --git a/source/blender/makesrna/intern/makesrna.c b/source/blender/makesrna/intern/makesrna.c
index 26ce24d5911..e197a8a3a4d 100644
--- a/source/blender/makesrna/intern/makesrna.c
+++ b/source/blender/makesrna/intern/makesrna.c
@@ -3445,7 +3445,7 @@ static void rna_generate(BlenderRNA *brna, FILE *f, const char *filename, const
 
 	/* we want the included C files to have warnings enabled but for the generated code
 	 * ignore unused-parameter warnings which are hard to prevent */
-#ifdef __GNUC__
+#if defined( __GNUC__) || defined(__clang__)
 	fprintf(f, "#pragma GCC diagnostic ignored \"-Wunused-parameter\"\n\n");
 #endif
 
diff --git a/source/blender/python/intern/stubs.c b/source/blender/python/intern/stubs.c
index cc186be60ea..3b3a4d6d2fe 100644
--- a/source/blender/python/intern/stubs.c
+++ b/source/blender/python/intern/stubs.c
@@ -32,7 +32,7 @@
 
 #include "BPY_extern.h"
 
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined(__clang__)
 #  pragma GCC diagnostic error "-Wmissing-prototypes"
 #  pragma GCC diagnostic ignored "-Wunused-parameter"
 #endif