Manual Dialog test: Fix compilation against Qt 4

Change-Id: I79a90cd252e99fb94c0429a3f03eb1ddacab1786
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

tests/manual/dialogs/main.cpp

@@ -80,12 +80,15 @@ MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
 
 int main(int argc, char *argv[])
 {
+#if QT_VERSION >= 0x050700
     for (int a = 1; a < argc; ++a) {
         if (!qstrcmp(argv[a], "-n")) {
             qDebug("AA_DontUseNativeDialogs");
             QCoreApplication::setAttribute(Qt::AA_DontUseNativeDialogs);
         }
     }
+#endif // Qt 5
+
     QApplication a(argc, argv);
     MainWindow w;
     w.move(500, 200);