With glibc 2.27 the openpty function prefers the TIOCGPTPEER ioctl.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <mvmbmhdosb9.fsf_-_@suse.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>