[clang] [WebAssembly,clang] Add __builtin_wasm_test_function_pointer_signature (PR #150201)

[Sam Clegg via cfe-commits]

sbc100 wrote:

> My thought is that it returns the return value. If one of the signatures matches it sets `*success = 1` otherwise it sets `*success = 0`. It probably can be written in terms of `__builtin_wasm_test_function_pointer_signature` with C++ templates but lot of projects I contribute to (e.g., Python) are written in C and not C++ so that's a bit inconvenient.

How would it work for functions that return different types?   i.e. how would `__builtin_wasm_test_function_pointer_signature` be polymorphic?

https://github.com/llvm/llvm-project/pull/150201