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

[Nuri Amari via llvm-commits]

NuriAmari wrote:

> Also the `-print-before/after` for the legacy PM is too complicated, it [adds a whole pass to print](https://github.com/llvm/llvm-project/blob/3e9c36303ca72929275fb97767af43b3aa04cab1/llvm/lib/IR/LegacyPassManager.cpp#L742) rather than checking if it should print right before/after running the pass (like what https://reviews.llvm.org/D133055 does). We should probably rewrite it to be simpler first.

Yeah my plan was just to modify the created passes, but that wasn't straight forward either from what I remember. I will see about simplifying it.

Thanks for the reviews all.

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