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

[Derek Schuff via llvm-commits]

dschuff wrote:

@sbc100 
Do you recall a particular reason that we have the linker synthesize the indirect call table rather than just making it weak? If so does that logic apply here too? Or why we synthesize it rather than linking in an object file that defines it to every program? (I guess for the last case, that's much less convenient than synthesizing it).

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