bug#38608: enable --fallback for the guix graphical installer

["Ludovic Courtès" <ludo@gnu.org>]

Brett Gilio <brettg@gnu.org> skribis:

> Nathan Dehnel <ncdehnel@gmail.com> writes:
>
>> I can't install guix because I keep getting substitute download errors.
>>
>> It's really punishing having to restart the install process after a
>> download error.
>>
>
> I actually don't know how our installer works that well, so I am going
> to leave the issue of whether to default to `--fallback` is the right
> decision to somebody else.
>
> However, for anybody reading this: does our installer dump logs
> anywhere? That seems like a more useful bit of information so we can
> triage and possibily fix why you are not receiving substitutes.

The “GUI” dumps logs in /tmp upon crashes, but in this case it’s not a
GUI issue, so there’s no log around.

Thanks,
Ludo’.