[CMake] Prune CMAKE_CXX_FLAGS stuff in llvm_process_sources.

It is the final step to deprecate contextual CMAKE_CXX_FLAGS.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200303 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed