[llvm] [CodeGen] [LIT] Addition of LIT mir testcases for pre-commit test. (PR #102128)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Title is verbose and doesn't state what the tests are for. This is also a case where it would be preferably to show the change from a starting IR test, since it's a full optimization pipeline issue 

https://github.com/llvm/llvm-project/pull/102128