Re-commit r187637: "clang-cl: add more options"

> This adds a bunch of options to clang-cl. Notably, this includes
> all the options that get passed when doing a default build of a
> command-line project with msbuild.exe in Debug and Release modes,
> and I believe all flags from Reid's original patch.

The original commit was reverted in r187640 after it broke the Mac build.

This should now be fixed, by Clang r187668, LLVM r187675, and putting
a -- before %s in the test.