[llvm] [WebAssembly] Enable multivalue return when multivalue ABI is used (PR #88492)

[Heejin Ahn via llvm-commits]

aheejin wrote:

> Maybe I can adjust `canLowerMultivalueReturn()` to remove the `usesMultivalueABI` logic and things will work the way before for us; is this a silly hack, do there exist a more principled way to do it? Thanks a lot in advance.

If what you want is to achieve the same multivalue-return-lowering behavior without passing `-Xclang -target-abi -Xclang experimental-mv`, I think what you said here is basically the simplest hack to do it. Or you can add `-target-abi experimental-mv` in clang driver programatically whenever `-mmultivalue` is given, but I'm not sure if this is a better hack than what you said.

https://github.com/llvm/llvm-project/pull/88492