clang-cl: Make the driver parse all(?) msvc flags

Even if we don't support a flag, we should be able to parse it
to provide a better error message than the current default
"error: no such file or directory: '/foo'" (which we should probably
also tweak, btw).

This also tries to clean up the test file a bit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194837 91177308-0d34-0410-b5e6-96231b3b80d8