[CMake] Add partial support for MSVC in compiler-rt builtins

[roman.shirokiy]

Summary

This enables MSVC build of complex number arithmetic compiler-rt builtins.

Related driver patch:
http://reviews.llvm.org/D17453

Consider Clang which is built under native Windows environment. Compiling the following code will result in "unresolved external symbol __divsc3 referenced in function main"

int main(){

float _Complex a, b, c;
c = a / b;
return 0;

}

Clang front-end generates calls to complex number arithmetic functions, which are nowhere to be found in Microsoft runtime libs. The idea of this patch is to enable MSVC build of compiler-rt builtins library with certain subset of ported-to-CL sources and link this lib in case if user has explicitly demanded so through "--rtlib" option. This will allow to compile code with usage of complex number arithmetic in general and spec2006/462.libquantum in particular.

[beanz]

Looks good to me.

compiler-rt/trunk/CMakeLists.txt

 append_list_if(COMPILER_RT_HAS_FNO_LTO_FLAG -fno-lto SANITIZER_COMMON_CFLAGS)
 
 if(MSVC)
   # Replace the /M[DT][d] flags with /MT, and strip any definitions of _DEBUG,
   # which cause definition mismatches at link time.
   # FIXME: In fact, sanitizers should support both /MT and /MD, see PR20214.
   if(COMPILER_RT_HAS_MT_FLAG)
     foreach(flag_var
+      CMAKE_C_FLAGS CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_RELEASE
+      CMAKE_C_FLAGS_MINSIZEREL CMAKE_C_FLAGS_RELWITHDEBINFO
       CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
       CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
       string(REGEX REPLACE "/M[DT]d" "/MT" ${flag_var} "${${flag_var}}")
       string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
       string(REGEX REPLACE "/D_DEBUG" "" ${flag_var} "${${flag_var}}")
     endforeach()
   endif()
   append_list_if(COMPILER_RT_HAS_Oy_FLAG /Oy- SANITIZER_COMMON_CFLAGS)

compiler-rt/trunk/lib/builtins/CMakeLists.txt

set(GENERIC_SOURCES
   udivmodsi4.c
   udivmodti4.c
   udivsi3.c
   udivti3.c
   umoddi3.c
   umodsi3.c
   umodti3.c)
 
+set(MSVC_SOURCES
+ divsc3.c
+ divdc3.c
+ divxc3.c
+ mulsc3.c
+ muldc3.c
+ mulxc3.c)
+
+
 if(APPLE)
   set(GENERIC_SOURCES
     ${GENERIC_SOURCES}
     atomic_flag_clear.c
     atomic_flag_clear_explicit.c
     atomic_flag_test_and_set.c
     atomic_flag_test_and_set_explicit.c
     atomic_signal_fence.c
set(i386_SOURCES
         i386/chkstk.S
         i386/chkstk2.S)
   endif()
 
   set(i686_SOURCES
       ${i386_SOURCES})
 else () # MSVC
   # Use C versions of functions when building on MSVC
-  # MSVC's assembler takes Intel syntax, not AT&T syntax
+  # MSVC's assembler takes Intel syntax, not AT&T syntax.
+  # Also use only MSVC compilable builtin implementations.
   set(x86_64_SOURCES
       x86_64/floatdidf.c
       x86_64/floatdisf.c
       x86_64/floatdixf.c
-      ${GENERIC_SOURCES})
+      ${MSVC_SOURCES})
   set(x86_64h_SOURCES ${x86_64_SOURCES})
-  set(i386_SOURCES ${GENERIC_SOURCES})
+  set(i386_SOURCES ${MSVC_SOURCES})
   set(i686_SOURCES ${i386_SOURCES})
 endif () # if (NOT MSVC)
 
 set(arm_SOURCES
   arm/adddf3vfp.S
   arm/addsf3vfp.S
   arm/aeabi_cdcmp.S
   arm/aeabi_cdcmpeq_check_nan.c

 set(wasm64_SOURCES ${GENERIC_SOURCES})
 
 add_custom_target(builtins)
 
 if (APPLE)
   add_subdirectory(Darwin-excludes)
   add_subdirectory(macho_embedded)
   darwin_add_builtin_libraries(${BUILTIN_SUPPORTED_OS})
-elseif (NOT WIN32 OR MINGW)
+else ()
   append_string_if(COMPILER_RT_HAS_STD_C99_FLAG -std=c99 maybe_stdc99)
 
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if (CAN_TARGET_${arch})
       # Filter out generic versions of routines that are re-implemented in
       # architecture specific manner.  This prevents multiple definitions of the
       # same symbols, making the symbol selection non-deterministic.
       foreach (_file ${${arch}_SOURCES})