pinentry_mac: add cf-private

    Undefined symbols for architecture x86_64:
      "_OBJC_CLASS_$_NSArray", referenced from:
          objc-class-ref in GPGDefaults.o
      "_OBJC_CLASS_$_NSDictionary", referenced from:
          objc-class-ref in PinentryController.o
          objc-class-ref in GPGDefaults.o
          objc-class-ref in KeychainSupport.o
      "_OBJC_CLASS_$_NSMutableDictionary", referenced from:
          objc-class-ref in GPGDefaults.o
      "_OBJC_CLASS_$_NSSet", referenced from:
          objc-class-ref in GPGDefaults.o
      "_OBJC_CLASS_$_NSUserDefaults", referenced from:
          objc-class-ref in GPGDefaults.o
    ld: symbol(s) not found for architecture x86_64