[llvm] [WebAssembly] Add more tests for `wasm-fix-irreducible-control-flow`. NFC (PR #181254)

[Demetrius Kanios via llvm-commits]

QuantumSegfault wrote:

Okay. I think I've settled on a good-enough generator that gives us both a random CFG of customizable size, but also starts with some guaranteed irreducibility, without too much complexity. Thoughts?

https://gist.github.com/QuantumSegfault/75effe1726ed2e22f42c3013a0cadb05

https://github.com/llvm/llvm-project/pull/181254