[llvm] [ConstraintElim] Add missing check to make sure the bound is loop-invariant (PR #70555)

[Florian Hahn via llvm-commits]

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

Still LGTM, thanks for adding the extra tests.

Feel free to merge the change once the test names are update

https://github.com/llvm/llvm-project/pull/70555