[llvm] [CodeGenPrepare] Folding `urem` with loop invariant value as remainder (PR #96625)

[via llvm-commits]

goldsteinn wrote:

> Should we drop the `CodeGen/X86` tests?

I kept them because the pipeline isn't quite the same as what we get w/ just `--loop-simplify -cogegenprepare`

https://github.com/llvm/llvm-project/pull/96625