Undefined symbols for architecture arm64:

Undefined symbols for architecture arm64:

  "_OBJC_CLASS_$_UIResponder", referenced from:

      _OBJC_CLASS_$_AppDelegate in AppDelegate.o

  "_OBJC_METACLASS_$_UIResponder", referenced from:

      _OBJC_METACLASS_$_AppDelegate in AppDelegate.o

  "_UIApplicationMain", referenced from:

      _main in main.o

  "_OBJC_METACLASS_$_UIViewController", referenced from:

      _OBJC_METACLASS_$_LoadingViewController in LoadingViewController.o

  "_OBJC_CLASS_$_UIViewController", referenced from:

      _OBJC_CLASS_$_LoadingViewController in LoadingViewController.o

ld: symbol(s) not found for architecture arm64

clang: error: linker command failed with exit code 1 (use -v to see invocation)