Hi,

Looking at <https://github.com/0xbb/gpu-switch/blob/master/gpu-switch>,
it appears that it uses 'chattr', 'mount', 'grep', 'cat' and
'basename'. So the corresponding packages would need to be added
to 'inputs' and a few 'substitute*' are required such that gpu-switch
doesn't require 'chattr' & friends to be in the environment.

/sys/firmware/efi/efivars is rather Linux-specific, presumably
non-existent on the hurd, so the hurd systems need to be removed from
supported-systems.

> +    (name "gpu-switch")
> +    (version "2017-04-28")
> +    (source
> +     (origin
> +       (method git-fetch)
> +       (uri (git-reference
> +             (url "https://github.com/0xbb/gpu-switch")
> +             (commit "a365f56d435c8ef84c4dd2ab935ede4992359e31")))

Where did you get this version/commit pair from? I'm not seeing it on
<https://github.com/0xbb/gpu-switch/releases>.

Greetings,
Maxime.