These are GNU extensions so they need to be behind _GNU_SOURCE. Fixes #16371.
Signed-off-by: Zoltán Mizsei <zmizsei@extrowerk.com> Change-Id: I44b39e8d76dd970e18e285b5d8b9bad715608154 Reviewed-on: https://review.haiku-os.org/715 Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>