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

[Hood Chatham via cfe-commits]

hoodmane wrote:

It seems that builtins can do that. In `SemaWasm.cpp` we call `TheCall->setType(FuncTy->getReturnType());` and that implies that the return type of the call to `__builtin_wasm_nontrapping_call()` is the same as the return type of `func`.

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