Add `-target x86_64-apple-darwin' to the compiler-rt overridden CFLAGS

diff --git a/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake b/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
index 28d398672..aac68bf36 100644
--- a/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
+++ b/compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake
@@ -265,7 +265,7 @@ endfunction()
 macro(darwin_add_builtin_libraries)
   set(DARWIN_EXCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/Darwin-excludes)
 
-  set(CFLAGS "-fPIC -O3 -fvisibility=hidden -DVISIBILITY_HIDDEN -Wall -fomit-frame-pointer")
+  set(CFLAGS "-fPIC -O3 -fvisibility=hidden -DVISIBILITY_HIDDEN -Wall -fomit-frame-pointer -target ${LLVM_DEFAULT_TARGET_TRIPLE} -isysroot ${CMAKE_OSX_SYSROOT} -I${CMAKE_OSX_SYSROOT}/usr/include")
   set(CMAKE_C_FLAGS "")
   set(CMAKE_CXX_FLAGS "")
   set(CMAKE_ASM_FLAGS "")
