build: Add GLib requirement

For consistency with other components and for the GLib macros set by
XDT_CHECK_PACKAGE when building with xfce4-dev-tools >= 4.17.1.

configure.ac.in

@@ -71,6 +71,7 @@ XDT_I18N([@LINGUAS@])
 dnl ***********************************
 dnl *** Check for required packages ***
 dnl ***********************************
+XDT_CHECK_PACKAGE([GLIB], [glib-2.0], [2.50.0])
 XDT_CHECK_PACKAGE([GTK], [gtk+-3.0], [3.20.0])
 XDT_CHECK_PACKAGE([LIBXFCE4PANEL], [libxfce4panel-2.0], [4.12.0])
 XDT_CHECK_PACKAGE([LIBXFCE4UTIL], [libxfce4util-1.0], [4.12.0])

panel-plugin/xkb-cairo.c

@@ -23,6 +23,10 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include <libxfce4util/libxfce4util.h>
 
 #include "xkb-cairo.h"

panel-plugin/xkb-keyboard.c

@@ -23,6 +23,10 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include "xkb-keyboard.h"
 #include "xkb-util.h"
 

panel-plugin/xkb-modifier.c

@@ -20,6 +20,10 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include "xkb-modifier.h"
 
 #include <gdk/gdk.h>

panel-plugin/xkb-util.c

@@ -23,6 +23,10 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include <string.h>
 
 #include "xkb-util.h"