[llvm] [WebAssembly] Reapply "[WebAssembly] Incorporate SCCs into WebAssemblyFixIrreducibleControlFlow" (#181755) (PR #184441)

[Heejin Ahn via llvm-commits]

aheejin wrote:

Whichever way we end up resolving this, can you add your reduced testcase to tests?
```ll
target triple = "wasm32-unknown-unknown"

define void @test() {
entry:
 switch i32 poison, label %b [
    i32 0, label %a
  ]

a:
  ret void

b:
    unreachable
}
```

https://github.com/llvm/llvm-project/pull/184441