bug#73435: gzdoom package probably depends on non-free files forbidding commercial distribution

[Mamao--- via Bug reports for GNU Guix <bug-guix@gnu.org>]

https://zdoom.org/wiki/License talks about files included in GZDoom that
forbid verbatim commercial distribution, violating GNU FSDG, which
demands that even data not serving practical purpose must allow
commercial distribution.

After trying to delete all the files in GZDoom forbidding commercial
distribution, I was unable to get GZDoom working so it seems that these
files are a hard requirement of GZDoom and that GZDoom won't work
without them. I believe these files are found in
/usr(/local)/share/games/doom/ after GZDoom is installed, but I'm not
sure. The package for Guix says:

"-DGUIX_OUT_PK3=\\\"" out "/share/games/doom\\\""

I've even tried to stop the generation of these files during compile
time to see if that would help gzdoom work without them, but that broke
compilation.

Since gzdoom doesn't seem to work without these non-free files, that
arguably makes gzdoom proprietary software because commercial verbatim
distribution is forbidden when these files are in place. If gzdoom is
proprietary software, then the freedoom package is violating the FSDG as
it strongly recommends gzdoom in its documentation, therefore to make
freedoom FSDG-compliant would likely shunning the recommendation for
gzdoom. This issue affects not only Guix System but also other
FSDG-compliant distros, because e.g. PureOS and Trisquel also ship
Freedoom with the recommendation to use gzdoom.

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