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

[Heejin Ahn via llvm-commits]

aheejin wrote:

@TerrorJack But wouldn't it be easier to just modify your build system command and add `-Xclang -target-abi -Xclang experimental-mv` than do a hacky modification in the source code after all?

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