compile fix if no QFileSystemWatcher is available

Change-Id: I22d0cd90da96e6b6f651768955c7f445dfbcf6bc
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>