[libegg] Include gdkx.h for gdk_x11_set_sm_client_id().

[Murray Cumming <murrayc src gnome org>]

commit c7b7ff9533898c6a7b63a6b6982d1ebc8e1823e7
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Dec 16 21:06:55 2016 +0100

    Include gdkx.h for gdk_x11_set_sm_client_id().

 libegg/smclient/eggsmclient-dbus.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/libegg/smclient/eggsmclient-dbus.c b/libegg/smclient/eggsmclient-dbus.c
index 30b2ca0..3d2add2 100644
--- a/libegg/smclient/eggsmclient-dbus.c
+++ b/libegg/smclient/eggsmclient-dbus.c
@@ -31,6 +31,7 @@
 #include <unistd.h>
 
 #include <gdk/gdk.h>
+#include <gdk/gdkx.h>
 #include <dbus/dbus-glib.h>
 
 #define GSM_DBUS_NAME      "org.gnome.SessionManager"