[clang] Add flags to dump IR to a file before and after LLVM passes (PR #65179)

[Nuri Amari via cfe-commits]

NuriAmari wrote:

I've tried this on a real application, and the output paths quickly get extremely long. So long that we fail to create the directory structure. Perhaps the nesting idea isn't the right choice after all.

https://github.com/llvm/llvm-project/pull/65179