Index: llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
@@ -381,6 +381,7 @@
 
 elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
   append_if(LLVM_ENABLE_WERROR "-Werror" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append_if(LLVM_ENABLE_WERROR "-Wno-error" CMAKE_REQUIRED_FLAGS)
   add_flag_if_supported("-Werror=date-time" WERROR_DATE_TIME)
   if (LLVM_ENABLE_CXX1Y)
     check_cxx_compiler_flag("-std=c++1y" CXX_SUPPORTS_CXX1Y)