emacs-guix: Requires GUILE_LOAD_(COMPILED_)PATH env vars (or "guile" package)

Hi! I have `emacs-guix` in a separate Guix profile with all Emacs stuff,

running on a foreign distro. I noticed that removing the `guile` package

(from all profiles) broke `emacs-guix` after a session restart, and that

restoring the `guile` package or just Guile's environment variables fixed the

issue:

```

$ nog # a script of mine running a distro shell with no Guix variables

$ . ~/env/guix/ivan/emacs/etc/profile # from profile with Emacs stuff

$ . ~/.config/guix/current/etc/profile

$ command -v guile || echo missing

missing

$ emacs

Running M-x guix then v yields this error:

Starting Guix REPL ... [5 times]

guix-geiser-eval: Error in evaluating guile expression: ice-9/boot-9.scm:1685:16: In procedure raise-exception:

Unbound variable: %max-returned-list-size

$ realpath ~/env/guix/ivan/emacs

/gnu/store/ahq…-profile

$ export GUILE_LOAD_PATH=/gnu/store/ahq…-profile/share/guile/site/3.0

$ export GUILE_LOAD_COMPILED_PATH=/gnu/store/ahq…-profile/lib/guile/3.0/site-ccache:/gnu/store/ahq…-profile/share/guile/site/3.0

$ emacs

Running M-x guix works successfully.

$ exit

```

I'm no Guix packaging expert, but it looks like `emacs-guix` should either

have `guile` as propagated input, or somehow add `GUILE_LOAD_PATH` and

`GUILE_LOAD_COMPILED_PATH` to the profile's search paths.

Thank you very much!

--

Ivan Vilata i Balaguer -- https://elvil.net/