[llvm] [FixIrreducible][UnifyLoopExits] Support switch statements (PR #206567)

[via llvm-commits]

hertelukas wrote:

Ah, true, my oversight; yes, I had to change exactly the same lines corresponding to the `callbr.ll` test. I rebased twice now due to merge conflicts, as there seems to be going on a lot with Cycles, but should be good to go now. I also ran with `-DLLVM_ENABLE_EXPENSIVE_CHECKS=ON` locally, and everything passed.

https://github.com/llvm/llvm-project/pull/206567