NFC: Ignore -Wreceiver-forward-class warning in SwiftObject.mm.

Author: tshortli

stdlib/public/runtime/SwiftObject.mm

@@ -1171,7 +1171,10 @@ static bool isObjCForUnownedReference(void *value) {
   if (object == nullptr)
     return nullptr;
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wreceiver-forward-class"
   if ([id_const_cast(object) isKindOfClass:[__SwiftValue class]]) {
+#pragma clang diagnostic pop
     // Source is a `__SwiftValue` container
     // Unwrap, then use the most general casting machine to do the heavy lifting
     auto typeValue = getValueFromSwiftValue(reinterpret_cast<__SwiftValue *>(object));