gentoo & QtCreator: suddenly qt_version_tag error!

I don't know why, all my Qml projects are giving me the error:

.obj/main.o:(.qtversion[qt_version_tag]+0x0): undefined reference to `qt_version_tag'

I don't really understand what the problem could be, since gcc is working well (I can build library using QtCreator) and there shouldn't be any relation between the Qt used in plasma and the Qt framework bundled with Qt package (v. 5.7.0)