[clang] [llvm] [WebAssembly] Represent reference types as TargetExtType (PR #203165)

[Demetrius Kanios via cfe-commits]

QuantumSegfault wrote:

> Incidentally, I noticed while writing this that we never emit `call_ref`. We should ideally check whether the `gc` target feature is present and if so emit a `call_ref` to call a function pointer rather than using a dummy table. I'll try to do this in a separate PR.

Way ahead of you. But maybe you can help push things forward.

#162227

It works, but in order to properly test it, I wanted to check against status quo. But status quo doesn't work at all. In order to fix existing thing, we need to move forward with #180900. Perhaps you have an opinion?

https://github.com/llvm/llvm-project/pull/203165