Calling vesc_tool from the Makefiles fails on some systems

[lukash]

E.g. on Ubuntu 20.04.6 LTS, a report from Siwoz on discord:

System setup:

 sudo apt update &&                \
 sudo apt upgrade -y &&            \
 sudo apt dist-upgrade -y &&       \
 sudo apt install -y               \
       git                         \
       make                        \
       libqt5gui5                  \
       libsdl2-2.0-0               \
       libgles2-mesa-dev           \

Build command:

cd ~/ &&                                                       \
git clone https://github.com/vedderb/vesc_pkg.git &&           \
cp /mnt/c/Users/slims/Downloads/vesc_tool_6.02 ~/vesc_tool &&  \
cd ~/vesc_pkg &&                                               \
make VESC_TOOL=~/vesc_tool

Error:

siwoz@Simon:~/vesc_pkg$ make VESC_TOOL=~/vesc_tool
make -C balance
make[1]: Entering directory '/home/siwoz/vesc_pkg/balance'
make -C balance
make[2]: Entering directory '/home/siwoz/vesc_pkg/balance/balance'
/home/siwoz/vesc_tool --xmlConfToCode conf/settings.xml
Done!
make[2]: Leaving directory '/home/siwoz/vesc_pkg/balance/balance'
/home/siwoz/vesc_tool --buildPkg "balance.vescpkg:balance.lisp:ui.qml:0:README.md:Balance"
qt.qpa.plugin: Could not find the Qt platform plugin "offscreen" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: xcb.

Aborted
make[1]: *** [Makefile:6: balance.vescpkg] Error 134
make[1]: Leaving directory '/home/siwoz/vesc_pkg/balance'
make: *** [Makefile:11: balance] Error 2 

Calling vesc_tool directly like this worked:

cd /home/siwoz/vesc_pkg/balance/balance && /home/siwoz/vesc_tool --xmlConfToCode conf/settings.xml

Seems there's a difference in env, perhaps something like export QT_PLUGIN_PATH could help, the thread on discord died off. Posting here the findings so far, so that someone else may have an easier time debugging this. Does not reproduce on my system.