Fix many warnings: #warning "Inclusion of header files from include/Qt is deprecated."

When using find_package(Qt4), QT_INCLUDES has include/QtCore before include/Qt
(as it should be) but somehow leads to -isystem for include/QtCore and -I for
include/Qt, so qglobal.h and others are picked up from include/Qt.

But we never hit this in KDE because we don't use find_package(Qt4) directly,
we let find_package(KDE4) take care of it, somehow it doesn't lead to -isystem.