Cygwin: timers: implement timerfd

First cut of a timerfd implementation.

Still TODO:
- fork/exec semantics
- timerfd_settime TFD_TIMER_CANCEL_ON_SET flag
- ioctl(TFD_IOC_SET_TICKS)
- bug fixes

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/dtable.cc

@@ -578,6 +578,9 @@ fh_alloc (path_conv& pc)
 	case FH_SIGNALFD:
 	  fh = cnew (fhandler_signalfd);
 	  break;
+	case FH_TIMERFD:
+	  fh = cnew (fhandler_timerfd);
+	  break;
 	case FH_TTY:
 	  if (!pc.isopen ())
 	    {