bug#26791: Hydra doesn't run make before using Guix

[Danny Milosavljevic]

For reference, the relevant commits are (newest first) 
360874dd1c1aafddd82e389b9da09f69bddb2a20 (not really suspicious), 
7e3f7acbe0885fd8a6e509fd0c309d1f4d9d3097, 
bf8b09169c7d8ae48ac99ea237b82867ee9aa885, 
370ae085b5107a0928fd744a987fb4070bdf6a00, 
83071b052a0585f7166245b7ba793436e104f8fe, 
0315abe608007f1fed96cdcae21b6a83902b25e6, 
9530e73b496fefe65dcb936825b6beda79f7fdf2, 
33f0aa88155ee0718f21e7de24eb539cb9872217, 
40fad1c24ce60076e26f6dc8096e4716d31d90c3 (!).

Note that this all works fine after Guix has been built using make, so I don't 
think the problem is in the source code of Guix.

As for that Hydra job:

>Switched to a new branch 'fetchgit'
>;;; compiled 
>/home/hydra/.cache/guile/ccache/2.0-LE-8-2.0/usr/local/bin/hydra-eval-guile-jobs.go
>adding `/gnu/store/vsw3112dw48ai5arsxf1qsvma8y4fvqp-git-export' to the load 
>path
>;;; compiling 
>/gnu/store/vsw3112dw48ai5arsxf1qsvma8y4fvqp-git-export/build-aux/hydra/../../gnu/packages/xnee.scm

It seems that hydra auto-compiles some Guix modules:

So this Hydra job should run make in 
/gnu/store/vsw3112dw48ai5arsxf1qsvma8y4fvqp-git-export first.

Unfortunately, I have no idea about Hydra - and "grep -r fetchgit ." inside 
"guix" doesn't turn up anything either.