It would be nice if it is more clearly specified what all thing has changed from Qt 4 to Qt5.
People using Qt4 since long tend to configure with many options like -no-exceptions:-no-stl: -no-qt3support:-no-xmlpatterns:-no-phonon:-no-phonon-backend: -no-svg: -no-webkit:-no-scripttools:-qt-libtiff: -qt-libmng: -no-multimedia: -no-script:-no-scripttool

and end up with failed configure.
The existing document (portingguide.html) is not very detailed.