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

[Sharadh Rajaraman via cfe-commits]

sharadhr wrote:

> I think this patch needs to go back to the drawing board.

I agree. `/Fo` is strictly for object files—that is, `.obj` as a result of a compilation—that is, `/c`, whereas `-o` is meant for 'any output'. 

My understanding is that @Arthapz made `/clang:-o` work with upstream, even without this patch. CMake needs to rework its understanding of the Clang compilation model and perhaps rework its invocation of BMI compilation and `clang-scan-deps`.

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