[llvm] [WebAssembly] Refactor PerformSETCCCombine (PR #144875)

[Thomas Lively via llvm-commits]

https://github.com/tlively approved this pull request.

Refactor LGTM. I don't have much of an opinion on whether this should use a template or not.

https://github.com/llvm/llvm-project/pull/144875