A few small cleanups to r187504. Thanks to dblaikie for the assist.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187521 91177308-0d34-0410-b5e6-96231b3b80d8
clang-cl: add the /c, /W0 and /W1 options

This adds a few more clang-cl options. It also exposes two core clang
options to the clang-cl mode: we need to be able to claim --driver_mode
so it doesn't show up as unused in cl mode, and we need -### for tests.

Differential Revision: http://llvm-reviews.chandlerc.com/D1232

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187527 91177308-0d34-0410-b5e6-96231b3b80d8