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

[via llvm-commits]

goldsteinn wrote:

No bug was different:
```
-  Builder.SetInsertPoint(LoopIncrPN);
+  Builder.SetInsertPoint(Rem);
```

If the loop was multiple BBs we would be inserting rem in wrong locations...

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