[llvm] WebAssembly: Stop directly using RuntimeLibcalls.def (PR #143054)

[Dan Gohman via llvm-commits]

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

This looks reasonable to me. It seems unlikely that we'd add major new subtarget-specific builtins any time soon.

https://github.com/llvm/llvm-project/pull/143054