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

[via cfe-commits]

h-vetinari wrote:

> given how important this it, I hope we can make this for clang21. Thanks!

FYI, branching for LLVM v21 is less than [two weeks away](https://discourse.llvm.org/t/llvm-21-x-release-information-and-branching/87065)




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