[CMake] pass -Wno-pedantic to cc_kext builtins build

We don't pass -pedantic to the builtin builds in the makefiles, so we shouldn't do it here. This is a temporary fix for the broken bot:

http://lab.llvm.org:8080/green/job/clang-stage1-cmake-RA_build/7526/warnings8Result/new/

A more correct solution is in the works.

llvm-svn: 248515

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

@@ -195,7 +195,7 @@ macro(darwin_add_builtin_libraries)
                               OS ${os}
                               ARCH ${arch}
                               SOURCES ${${arch}_SOURCES}
-                              CFLAGS "-std=c99" -arch ${arch} -mkernel
+                              CFLAGS "-std=c99" -arch ${arch} -mkernel -Wno-pedantic
                               DEFS KERNEL_USE
                               PARENT_TARGET builtins)