Thanks for the answer, I found another solution as well that worked for me.
It is probably more intuitive for experts, but i noticed that in the third party from your git you should also imply git submodule init and git submodule update .
After doing that, the old instructions worked semi-properly, and I could reinstall the voxl-portal package with not farther problems. It's just the README files that were not so obvious in explaining so.