seems i was wrong afterall: QResource::registerResource()
But you have to provide the resource binary (.rcc file). Created with the following command: rcc -binary myresource.qrc -o myresource.rcc
Okay... finally i solved it. Nothing to do with .pro file or PLUGIN macro. It was a basic PATH issue. qmake was searching for 'plugin' directory in /PREFIX path not in /SYSROOT/PREFIX path. I just copied all plugin directory from /SYSROOT/PREFIX to /PREFIX directory. I know this may not be the right way, but it temporarily solved my issue. If someone could suggest the correct solution please let me know.
Have you looked at the bug report in the other thread you were following? Apparently there were some bug in the static building for Qt 5.5 and it's fixed in Qt 5.6.1 (https://bugreports.qt.io/browse/QTBUG-51071). So aside from upgrading, am at a loss ...
ACGuiApplication is a symbol that comes from that other library so it's not provided by libCommon. Have a look at the link_prl and create_prl qmake options. They should provide you with all the dependencies needed automatically.