contacts: add cf-private

    Undefined symbols for architecture x86_64:
      "_OBJC_CLASS_$_NSArray", referenced from:
          objc-class-ref in contacts.o
          objc-class-ref in FormatHelper.o
      "_OBJC_CLASS_$_NSMutableArray", referenced from:
          objc-class-ref in FormatHelper.o
    ld: symbol(s) not found for architecture x86_64