[llvm] [LV] Apply urem folds to preheader (PR #213928)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM, test diffs looked as expected. I'm honestly not too concerned about the UTC churn, manually staging hunks doesn't sound like a good use of time if another UTC update down the line is going to rename them anyway. 

https://github.com/llvm/llvm-project/pull/213928