bug#30370: guix system init can't find guix-register

[Diego Nicola Barbato]

Hello Guix,

I tried to install GuixSD on a loop device (/dev/loop1) whith its main
partition mounted under /mnt like this:

$ guix system init /mnt/etc/config.scm /mnt

This failed with the following error message:

Betriebssystem unter »/mnt« wird initialisiert …
In execvp of 
/gnu/store/d4wwx93gqizx132zjk7h1ir7rzph0pig-guix-0.12.0-10.ba2260d/sbin/guix-register:
 Datei oder Verzeichnis nicht gefunden
copying to '/mnt'...
guix system: error: fport_write: Datenübergabe unterbrochen (broken pipe)

I run GuixSD on an x86_64 machine (commit:
a3a932c008d0d9051eb8cdfdcea07ebd7b68b1b3) and the configfile is a copy
of the `bare-bones.tmpl' with the target field in the
bootloader-configuration changed to "/dev/loop1".

Greetings

Diego