g_thread_init is deprecated

Since glib 2.32 this function is just an empty body.
Fix the warning and don't try to call it. There seems
to be no way to disable threading in glib.

Change-Id: Id30e606d341bd6ef871737275336f6c6b3b2559b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>

src/corelib/kernel/qeventdispatcher_glib.cpp

@@ -293,12 +293,14 @@ static GSourceFuncs postEventSourceFuncs = {
 QEventDispatcherGlibPrivate::QEventDispatcherGlibPrivate(GMainContext *context)
     : mainContext(context)
 {
+#if GLIB_MAJOR_VERSION == 2 && GLIB_MINOR_VERSION < 32
     if (qEnvironmentVariableIsEmpty("QT_NO_THREADED_GLIB")) {
         static QBasicMutex mutex;
         QMutexLocker locker(&mutex);
         if (!g_thread_supported())
             g_thread_init(NULL);
     }
+#endif
 
     if (mainContext) {
         g_main_context_ref(mainContext);