QtDesigner/QtUiPlugin include order leads to deprecated compiler warnings

The following line "#include <QDesignerCustomWidgetInterface>" in application code leads to a compiler warning: "# warning Header <QtDesigner/QDesignerCustomWidgetInterface> is deprecated. Please include <QtUiPlugin/QDesignerCustomWidgetInterface> instead."

The reason for using the deprecated path is because of having an include path of "... -I/disk/local/Qt-5.6.0-beta/include/QtDesigner -I/disk/local/Qt-5.6.0-beta/include/QtUiPlugin" coming from the qmake spec files.

So here qmake is sending a warning about its own spec files, what doesn't make much sense as it could fix the situation instead.

My use case is the designer plugin of the Qwt library ( http://qwt.sf.net ). I can modify the include path in a new version of Qwt, but for users updating Qt to 5.6, but staying with an older version of Qwt these warnings ( already got support requests about this ) are irritating.