This adds a _cogl_poll_renderer_add_source() function that we can use
within cogl to hook into the mainloop without necessarily having a file
descriptor to poll. Since the intention is to use this to support
polling for fence completions this also updates the
CoglPollCheckCallback type to take a timeout pointer so sources can
optionally update the timeout that will be passed to poll.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 81c1ce0ffce4e75e08622e20848405987e00b3cc)
7b14b5e3da