Use AC_USE_SYSTEM_EXTENSIONS to get _GNU_SOURCE, _XOPEN_SOURCE etc.

Similar to Bug #684123 in GLib.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=641638
Bug-Debian: https://bugs.debian.org/756476
Reviewed-by: Matthias Clasen

configure.ac

@@ -227,6 +227,8 @@ LT_INIT([disable-static win32-dll])
 # Create libtool early, because it's used in configure
 LT_OUTPUT
 
+# Define _GNU_SOURCE etc. where appropriate, e.g. for strptime() on glibc
+AC_USE_SYSTEM_EXTENSIONS
 # Make sure we use 64-bit versions of various file stuff.
 AC_SYS_LARGEFILE
 

gdk/wayland/gdkdevice-wayland.c

@@ -15,7 +15,6 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#define _GNU_SOURCE
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>

gtk/fnmatch.c

@@ -35,13 +35,6 @@
 
 #include <glib.h>
 
-/* We need to make sure that all constants are defined
- * to properly compile this file
- */
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
-
 static gunichar
 get_char (const char **str)
 {

gtk/gtkscalebutton.c

@@ -36,9 +36,6 @@
 
 #include "gtkscalebutton.h"
 
-#ifndef _WIN32
-#define _GNU_SOURCE
-#endif
 #include <math.h>
 #include <stdlib.h>
 #include <string.h>

gtk/gtksearchenginesimple.c

@@ -21,14 +21,6 @@
 
 #include "config.h"
 
-/* these must be defined even when HAVE_GNU_FTW is not defined
- * because (really) old versions of GNU libc have ftw.h but do
- * export ftw() and friends only if _XOPEN_SOURCE and _GNU_SOURCE
- * are defined. see bug #444097.
- */
-#define _XOPEN_SOURCE 600
-#define _GNU_SOURCE
-
 #ifdef HAVE_FTW_H
 #include <ftw.h>
 #endif

modules/printbackends/cups/gtkprintbackendcups.c

@@ -17,10 +17,6 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifdef __linux__
-#define _GNU_SOURCE
-#endif
-
 #include "config.h"
 #include <ctype.h>
 #include <unistd.h>