Use AC_USE_SYSTEM_EXTENSIONS instead of #define _GNU_SOURCE

It's less copy/paste, works everywhere, etc.

Also fix some missing #include "config.h".

configure.ac

@@ -7,6 +7,7 @@ AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([1.11 -Wno-portability foreign no-define tar-ustar no-dist-gzip dist-xz])
 AM_MAINTAINER_MODE([enable])
 AM_SILENT_RULES([yes])
+AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
 
 AC_PROG_CC

src/libostree/ostree-core.c

@@ -20,9 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-/* for mkdtemp */
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"

src/libostree/ostree-diff.c

@@ -20,8 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"

src/libostree/ostree-repo-traverse.c

@@ -20,8 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
-
 #include "config.h"
 
 #include "ostree.h"

src/libotutil/ot-unix-utils.c

@@ -22,8 +22,6 @@
 
 #include "config.h"
 
-#define _GNU_SOURCE
-
 #include "otutil.h"
 
 #include <gio/gio.h>

src/ostree/ot-admin-cleanup.c

@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"

src/ostree/ot-admin-functions.c

@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"

src/ostree/ot-admin-util.c

@@ -20,7 +20,6 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
 #include "config.h"
 
 #include "ot-admin-functions.h"

src/switchroot/ostree-mount-util.c

@@ -20,7 +20,7 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
+#include "config.h"
 
 #include <stdarg.h>
 #include <errno.h>

src/switchroot/ostree-prepare-root.c

@@ -23,7 +23,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-#define _GNU_SOURCE
+
+#include "config.h"
+
 #include <sys/mount.h>
 #include <sys/types.h>
 #include <sys/stat.h>

src/switchroot/ostree-remount.c

@@ -20,7 +20,7 @@
  * Author: Colin Walters <walters@verbum.org>
  */
 
-#define _GNU_SOURCE
+#include "config.h"
 
 #include <string.h>
 #include <stdio.h>