I committed this to my source tree pending the next release.
A commit references this bug:
Date: Fri Apr 5 13:25:13 UTC 2019
New revision: 497951
Update to 2.18.9.
* Add check for sensible CMAKE settings to ports-mgmt/portlint 
* Do not warn about absolute paths in *_OLD_CMD (when USES=shebangfix is set) 
* If an option only has QMAKE_ON or QMAKE_OFF settings, it is flagged as no effect 
* Check for options defined per ARCH to make sure we don't have a lot
of false positives. 
(Note:  was already in PORTREVISION 2).
PR: 232948 
Submitted by: adridg 
Fixed in 2.18.9.