Rollup merge of #152787 - scottmcm:alignment-checks-test, r=jieyouxu

Add a mir-opt test for alignment check generation [zero changes outside tests]

I wrote this as part of rust-lang/rust#152641 which it looks like I'm going to just close, so submitting the new test separately since we didn't have any mir-opt testing of this pass that I could find (at least `x test tests/mir-opt` didn't fail when I broke them) so figured it's something that should exist.

Author: JonathanBrouwer