Found the source of the build issues. This line in voxl-mpa-to-ros2
python3 -m pip install colcon-common-extensions lark
is installing an incompatible version of empy. See here:
https://github.com/colcon/colcon-core/issues/602
Another issue with a default sentinel/voxl2 set-up when installing ros2 I've found - need to add a sim link for libtinyxml2. I got this build error
make[2]: *** No rule to make target '/usr/lib/aarch64-linux-gnu/libtinyxml2.so', needed by 'libpx4_msgs__rosidl_typesupport_fastrtps_cpp.so'. Stop
which I resolved via
ln -s /usr/lib/aarch64-linux-gnu/libtinyxml2.so.6 /usr/lib/aarch64-linux-gnu/libtinyxml2.so
I don't know if these issues are specific to the sentinel platform or not. I added the empy version fix to a fork of voxl-mpa-to-ros2 and will push a merge request. I'm guessing there should be a similar fix within a voxl-ros2-foxy install script or else there'll be build issues whenever trying to build a ros package onboard a vehicle that compiles ros messages (empy version issue was what was preventing me from building px4_msgs package onboard)