Similar to QtWidgets ensure that QGuiApplication::notify() is always
called via its exported symbols. This is needed to allow overloading it
via LD_PRELOAD or other means.

Change-Id: I84d0176b984c5fdf9b199127e08fcfa93dbc853f
Reviewed-by: Harri Porten <porten@froglogic.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>