Rework ppc options handling into a features group.

This should have no functional behavior.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192838 91177308-0d34-0410-b5e6-96231b3b80d8
Add minimal command line support for the VSX powerpc processor.

Preprocessor support is still needed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192839 91177308-0d34-0410-b5e6-96231b3b80d8