A struct for describing the state of a file descriptor that Cogl needs to block on.
events field contains a bitmask of PollFDEvent<!-- -->s that
should cause the application to wake up. After the application is woken up from idle it should pass back an array of
PollFD<!-- -->s to Cogl and update the
revents mask to the actual events that occurred on the file descriptor.
Note that CoglPollFD is deliberately exactly the same as struct pollfd on Unix so that it can simply be cast when calling poll.