[clang] Accept `cl`-style output arguments (`/Fo`, `-Fo`) for `--fmodule-output` (PR #121046)

[Sharadh Rajaraman via cfe-commits]

sharadhr wrote:

I think I need to be a little more nuanced—with my changes, PCHs requested with `/Fo` and `/Fp` aren't output, causing the PCH test failures.

https://github.com/llvm/llvm-project/pull/121046