[llvm] [WebAssembly] Replace Reachability with SCCs in Irreducible CFG Fixer (PR #179722)

[Demetrius Kanios via llvm-commits]

QuantumSegfault wrote:

Alright. I can open a new PR soon. 

I'm sifting through and seeing what else can be cleaned up now that we are using SCCs (e.g. I think it can remove the need for `LoopBlocks`).

So yeah, probably rerun the tests. "Fuzzing" maybe in the sense that I throw some random (or maybe not-so-random, if I can find a good patterns of irreducibility to generate) CFGs at it again. I don't think running it through `llvm-isel-fuzzer` again is worth it...need a more targeted CFG fuzzing.

https://github.com/llvm/llvm-project/pull/179722