I think the BROKEN flags in ports r473012 were in the window where lxqt-build-tools was updated to 0.5.0 and before x11-toolkits/qtermwidget was updated to 0.9.0.
that combination gives the mentioned error.
I've succesfully built qtermwidget 0.9.0 on raspberry pi 2.
I further tested 12 current armv7 and aarch64 12 current.
A commit references this bug:
Date: Sat Jul 7 19:36:04 UTC 2018
New revision: 474130
x11-toolkits/qtermwidget is not broken on armv6 armv7 or aarch64
Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D16173