function: Add support for wildcards in arguments.

We don't support unnamed arguments, and we give a terrible error
("Parameter has an unsupported type.") when you use them.

They're very simple to implement so we should just do it.

tests/expectations/function_args.cpp

@@ -9,4 +9,6 @@ void pointer_test(const uint64_t *a);
 
 void print_from_rust();
 
+void unnamed(const uint64_t*);
+
 } // extern "C"