From now on, ports that depend on Qt4 will have to set
USES= qt:4
USE_QT= foo bar
ports depending on Qt5 will use
USES= qt:5
USE_QT= foo bar
PR: 229225
Exp-run by: antoine
Reviewed by: mat
Approved by: portmgr (antoine)
Differential Revision: →https://reviews.freebsd.org/D15540