build: add the compatibility header for g_clear_pointer()

Necessary for GLib < 2.34

src/devices/adsl/nm-atm-manager.c

@@ -28,6 +28,7 @@
 #include "nm-device-adsl.h"
 #include "nm-device-factory.h"
 #include "nm-logging.h"
+#include "nm-glib-compat.h"
 
 typedef struct {
 	GUdevClient *client;

src/nm-active-connection.c

@@ -33,6 +33,7 @@
 #include "NetworkManagerUtils.h"
 #include "gsystem-local-alloc.h"
 #include "nm-active-connection-glue.h"
+#include "nm-glib-compat.h"
 
 /* Base class for anything implementing the Connection.Active D-Bus interface */
 G_DEFINE_ABSTRACT_TYPE (NMActiveConnection, nm_active_connection, G_TYPE_OBJECT)

src/settings/nm-settings-connection.c

@@ -37,6 +37,7 @@
 #include "NetworkManagerUtils.h"
 #include "nm-properties-changed-signal.h"
 #include "nm-core-internal.h"
+#include "nm-glib-compat.h"
 
 #define SETTINGS_TIMESTAMPS_FILE  NMSTATEDIR "/timestamps"
 #define SETTINGS_SEEN_BSSIDS_FILE NMSTATEDIR "/seen-bssids"