build: use compat version of g_clear_pointer()

Ubuntu 12.04 has an ancient version of glib, which we nevertheless support.

(cherry picked from commit eb2b8c2798)

src/main-utils.c

@@ -33,6 +33,8 @@
 #include <glib/gi18n.h>
 #include <gmodule.h>
 
+#include "nm-glib-compat.h"
+
 #include "gsystem-local-alloc.h"
 #include "main-utils.h"
 #include "nm-posix-signals.h"

src/nm-connectivity.c

@@ -26,6 +26,8 @@
 #include <libsoup/soup.h>
 #endif
 
+#include "nm-glib-compat.h"
+
 #include "nm-connectivity.h"
 #include "nm-config.h"
 #include "nm-logging.h"

src/supplicant-manager/nm-supplicant-manager.c

@@ -25,6 +25,8 @@
 #include <glib.h>
 #include <dbus/dbus.h>
 
+#include "nm-glib-compat.h"
+
 #include "nm-supplicant-manager.h"
 #include "nm-supplicant-interface.h"
 #include "nm-dbus-manager.h"