Index: HandleLLVMOptions.cmake
===================================================================
--- HandleLLVMOptions.cmake
+++ HandleLLVMOptions.cmake
@@ -202,7 +202,7 @@
   if (LLVM_ENABLE_WERROR)
     add_llvm_definitions( /WX )
   endif (LLVM_ENABLE_WERROR)
-elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
+elseif( MSVC )
   if (LLVM_ENABLE_WARNINGS)
     append("-Wall -W -Wno-unused-parameter -Wwrite-strings" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)