This looks like a GL vs GLES incompatibility: libqt5opengl uses OpenGL
ES on armel+armhf, simgear/flightgear use full OpenGL on all
architectures, and the two can't be mixed.
simgear+flightgear probably can't switch to OpenGL ES because they use
legacy OpenGL functions that aren't in ES. (They fail to build on
Ubuntu's GLES-only(?) armhf because of this:
https://launchpad.net/ubuntu/+source/simgear/1:2018.1.1+dfsg-1/+build/14785755/+files/buildlog_ubuntu-bionic-armhf.simgear_1%3A2018.1.1+dfsg-1_BUILDING.txt.gz
https://bugs.launchpad.net/ubuntu/+source/simgear/+bug/1423380 )
Given this, I suspect the best we can get on armel+armhf is a no-Qt
flightgear (i.e. no launcher etc - change -DENABLE_QT in debian/rules).
It must also continue to use openscenegraph 3.2 (OpenGL) rather than 3.4
(OpenGL ES on armel+armhf).
