examples: port qmake examples to new connection style

Task-number: QTBUG-106893
Change-Id: Ie4a4874359ac7750de344f4e3702ea7be09e7b53
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>

examples/qmake/precompile/main.cpp

@@ -15,7 +15,8 @@ int main(int argc, char **argv)
     MyObject obj;
     MyDialog dialog;
 
-    dialog.connect(dialog.aButton, SIGNAL(clicked()), SLOT(close()));
+    QObject::connect(dialog.aButton, &QPushButton::clicked,
+                     &dialog, &MyDialog::close);
     dialog.show();
 
     return app.exec();