Undefined symbols for architecture x86_64:
"_CFNotificationCenterAddObserver", referenced from:
_main in main.o
"_CFNotificationCenterGetDistributedCenter", referenced from:
_main in main.o
"_OBJC_CLASS_$_NSTimer", referenced from:
objc-class-ref in main.o
objc-class-ref in x-screen.o
"_OBJC_EHTYPE_$_NSException", referenced from:
GCC_except_table25 in main.o
ld: symbol(s) not found for architecture x86_64
