Define _GNU_SOURCE not only on GNU/Hurd, but also other glibc-based platforms including GNU/kFreeBSD. See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826061#10 and https://salsa.debian.org/nginx-team/nginx/-/blob/master/debian/patches/0003-define_gnu_source-on-other-glibc-based-platforms.patch
Date: Sat, 16 Jul 2016 23:52:50 +0100 From: Steven Chamberlain <stevenc@debian.org> Subject: Use _GNU_SOURCE on GNU/kFreeBSD Forwarded: https://trac.nginx.org/nginx/ticket/2366
Define _GNU_SOURCE not only on GNU/Hurd, but also other glibc-based platforms including GNU/kFreeBSD.
