[clang-tools-extra] [llvm] [clang] [LLVM] Add IRNormalizer Pass (PR #68176)

[Justin Fargnoli via cfe-commits]

justinfargnoli wrote:

> I would recommend trying to run this pass (with all options enabled) over all existing tests to make sure that it doesn't cause any crashes/verifier failures. You're moving instructions around, and it's easy to get that wrong when invoke, callbr or catchswitch are involved.

Thanks for this suggestion! It helped iron out a lot of bugs in the implementation. 

> I would also try to add this pass at the end of the clang pipeline and run llvm-test-suite to verify that the normalization this does is indeed semantics-preserving.

I'm running into some linking errors when trying to build [`llvm-test-suite`](https://github.com/llvm/llvm-test-suite/tree/main). Pinging for another round of review in the meantime. 

https://github.com/llvm/llvm-project/pull/68176