[llvm] Wasm: add support for `swifttailcc` calling convention (PR #188296)

[Yuta Saito via llvm-commits]

kateinoigakukun wrote:

@dschuff Thanks for letting us know. I've started taking a look but I'll revert the change if it takes a day. 

https://github.com/llvm/llvm-project/pull/188296