poll/select: prevent busy-waiting

poll/select: prevent busy-waiting

2012-05-21  Paolo Bonzini  <bonzini@gnu.org>

	poll/select: prevent busy-waiting.  SwitchToThread() only gives away
	the rest of the current time slice to another thread in the current
	process. So if the thread that feeds the file decscriptor we're
	polling is not in the current process, we get busy-waiting.
	* lib/poll.c: Use SleepEx(1, TRUE) instead of SwitchToThread().
	Patch from Theodore Leblond.
	* lib/select.c: Split polling out of the loop that sets the output
	fd_sets.  Check for zero result and loop if the wait timeout is
	infinite.