notify_register_check(3) on macOS

The text e148bc02405e, as macOS 10.15.6, macOS 10.15.5, macOS 10.15.4, macOS 10.15.3, macOS 10.15.2, macOS 10.15.1, macOS 10.15 shipped it.

event distribution functions

notify_register_check(3) on macOS now