[clang] [Clang][WebAssembly] Fix WASM tables to allow `__funcref` function pointers (PR #178720)

[Paulo Matos via cfe-commits]

pmatos wrote:

> Requesting review
> 
> @dschuff @pmatos

Thanks - that's looking good to me.

Maybe you want to add more tests, like:
* https://github.com/pmatos/llvm-project/blob/09dbbdca70c3453eeb9c4bc2fcfd26c47be7a456/clang/test/CodeGen/WebAssembly/builtins-table-funcref.c
* https://github.com/pmatos/llvm-project/blob/09dbbdca70c3453eeb9c4bc2fcfd26c47be7a456/clang/test/Sema/wasm-funcref-table.c

https://github.com/llvm/llvm-project/pull/178720