[llvm] [LoongArch] Add a pass to rewrite rd to r0 for non-computational instrs whose return values are unused (PR #94590)

[via llvm-commits]

heiher wrote:

> Just checking in,
> 
> Thanks for the first test fix! 👍
> 
> Is there work being done on the second failure?

Oops. I overlooked that I didn't have assertions enabled locally, I'll fix that right away.

https://github.com/llvm/llvm-project/pull/94590