Add support to -Wa,-W in clang

Currently clang does not support -Wa,-W, which suppresses warning
messages in GNU assembler. Add this option for gcc compatibility.
https://bugs.llvm.org/show_bug.cgi?id=43651

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374822 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed