[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.
> 
> I've never experienced it myself, but my teammate has said another reason to want this is that when using thinLTO, multiple modules are processed concurrently on different threads, and the printed output can end up interleaved and be hard to read.
> 

Ah that makes sense


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