[NetworkManager-libreswan] build: enable -D_GNU_SOURCE everywhere

[Lubomir Rintel <lkundrak src gnome org>]

commit 27297fe8b98ff6f293d636c2af1f3016a62ade31
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Wed Oct 24 15:23:47 2018 +0200

    build: enable -D_GNU_SOURCE everywhere
    
    The shared files are GNU sources: they use glibc dynamic linker
    specialties.

 configure.ac               | 2 ++
 src/nm-libreswan-service.c | 2 --
 src/show-xfrm.c            | 1 -
 3 files changed, 2 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index d7047b1..58830c7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,6 +30,8 @@ AC_PROG_LIBTOOL
 AC_PROG_LN_S
 AC_PROG_MKDIR_P
 
+AC_GNU_SOURCE
+
 AC_CHECK_PROG([has_file], file, yes, no)
 if test x$has_file = xno ; then
     AC_MSG_ERROR(["file" utility not found.])
diff --git a/src/nm-libreswan-service.c b/src/nm-libreswan-service.c
index e69deb8..47175dc 100644
--- a/src/nm-libreswan-service.c
+++ b/src/nm-libreswan-service.c
@@ -24,8 +24,6 @@
 
 #include "nm-default.h"
 
-#define _GNU_SOURCE 1
-
 #include <netinet/in.h>
 #include <arpa/inet.h>
 
diff --git a/src/show-xfrm.c b/src/show-xfrm.c
index d5fb2c5..dfa3aec 100644
--- a/src/show-xfrm.c
+++ b/src/show-xfrm.c
@@ -18,7 +18,6 @@
 
 #include "nm-default.h"
 
-#define _GNU_SOURCE 1
 #include <netlink/netlink.h>
 #include <netlink/msg.h>
 #include <sys/socket.h>