[llvm] Add option to dump IR to files instead of stderr (PR #66412)

[Nuri Amari via llvm-commits]

NuriAmari wrote:

@aeubanks If I could ask quickly, what do you think the easiest way to test the same functionality but implemeted for the legacy pass manager would be?

Seems running `opt` with the legacy pass manager is no longer possible. Should I use `llc`, and if so is there a set of "no-op" like machine passes? Seems the original -print-after behavior was tested before the NPM came into the picture.

https://github.com/llvm/llvm-project/pull/66412