[CMake] Apply ADDITIONAL_HEADERS introduced in r199639.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@199640 91177308-0d34-0410-b5e6-96231b3b80d8
[ARM] Add ACLE enum/wchar size predefines

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@199642 91177308-0d34-0410-b5e6-96231b3b80d8