[llvm] [WebAssembly] Define `__funcref_call_table` in generated asm and objects (PR #180900)

[Sam Clegg via llvm-commits]

sbc100 wrote:

@hoodmane could you use a real `call_ref` in your use case?  i.e. do you have function references available?

https://github.com/llvm/llvm-project/pull/180900