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

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

I like this feature, though I feel like in many cases `-print-changed` is good enough.
Also slightly tangent: I think LLVM's interim github PR policy is to discourage force push on PR branch in favor of amending commits: https://discourse.llvm.org/t/update-on-github-pull-requests/71540/53

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