[NFC] Serialize ObjC selectors for protocols

The ObjCMethodLookupTable for protocols was not being serialized and rebuilt on load, so NominalTypeDecl::lookupDirect() on selectors was not working correctly for deserialized types. Correct this oversight.

lib/Serialization/ModuleFile.h

@@ -634,7 +634,7 @@ public:
   ///
   /// \param methods The list of @objc methods in this class that have this
   /// selector and are instance/class methods as requested.
-  void loadObjCMethods(ClassDecl *classDecl,
+  void loadObjCMethods(NominalTypeDecl *typeDecl,
                        ObjCSelector selector,
                        bool isInstanceMethod,
                        llvm::TinyPtrVector<AbstractFunctionDecl *> &methods);