jobserver: detect properly O_NONBLOCK

jobserver: detect properly O_NONBLOCK

	PR lto/106700

gcc/ChangeLog:

	* configure.ac: Detect O_NONBLOCK flag for open.
	* config.in: Regenerate.
	* configure: Regenerate.
	* opts-common.cc (jobserver_info::connect): Set is_connected
	  properly based on O_NONBLOCK.
	* opts-jobserver.h (struct jobserver_info): Add is_connected
	  member variable.

gcc/lto/ChangeLog:

	* lto.cc (wait_for_child): Ask if we are connected to jobserver.
	(stream_out_partitions): Likewise.