[bug#35653] [PATCH] gnu: Add rcm.

[Josh Holland]

Danny Milosavljevic writes:
> Yes, and it's not so important in which module what is.

I'll just leave it in its own module for now then, and if a maintainer
wants to move it either when it's merged or later down the line that's
fine.

> From your description, try (#:parallel-tests? #f) instead of (#:tests? #f).

Oh of course, that makes perfect sense!  That fixes it and all the tests
pass now.

> Some test scripts still have /bin/sh

AFAICT the only one I'm not patching is `test/rcup-standalone.t` and
that's kind of a weird one, because it's testing the feature to output a
standalone shell script rather than run it.  Changing that would require
patching the rcup script itself and I don't think that's worth it,
especially as the script uses the bash default value syntax to allow
all the commands to be overriden.

If I'm still operating git send-email correctly, a new patch should be
attached with these changes, and a better commit message.  I also updated
`gnu/local.mk` because that seems to be a thing I forgot initially.

Thanks,
Josh