(I can't use git-send-email with git installed from Guix for some
reason; it says subcommand not found.)

So here's 11 patches that add Mupen64Plus, the console front-end, and
many essential plugins.

These packages need to be used in a somewhat peculiar way:

- install *both* mupen64plus-core and mupen64plus-ui-console in your
  profile,

- install all the plugins in your profile,

- in your config file ($XDG_CONFIG_HOME/mupen64plus/mupen64plus.cfg),
  set Core/SharedDataPath to $guix_profile/share/mupen64plus, and set
  UI-Console/PluginDir to $guix_profile/lib/mupen64plus,

- specify your input/audio/video/rsp plugins of choice (for video, the
  Glide64 ones work well for me, and the HLE one for RSP).

That yields a working setup.  I don't know if I can make it work any
better out of the box (without horrible hacks and/or substantial patches
to the C code) because the whole system seems to assume the existence of
a single "shared data" and a single "plugin" directory, so a user is
best served by installing all preferred mupen64plus-* packages into one
profile and then pointing the data and plugin directories there as
described above.  In particular, the -core package needs to be installed
too (despite ui-console already closing over it) because it also
provides a data file without which some things don't work.

By the way, some video plugins don't work out of the box, and I don't
really know how to make them work or if they're entirely broken, but
they're packaged by Debian as well (with the same kinds of breakage out
of the box) so I also packaged them.