Freedom Issue #375
[virtualbox-libre] contains BIOS which needs a nonfree compiler to build from source
See the src/VBox/Devices/PC/BIOS directory in the source archive. The VBoxBiosAlternative.asm file is generated from C sources compiled using the OpenWatcom compiler which has a nonfree open source license (it is not included in Parabola).
dosemu is already blacklisted for the same reason.
Debian moved it to contrib, lembas reported it at https://trisquel.info/en/forum/virtualbox#comment-39916.
We should build it using a different compiler or remove the package (both Bochs BIOS and SeaBIOS are built using different, free, compilers).