bug#23807: guix build not respecting --keep-going

[Ethan J]

I've been attempting to use the "build all packages" one liner listed on https://www.gnu.org/software/guix/manual/html_node/Invoking-guix-build.html to populate my store for a local mirror however when guix fails to build a package it exits and stops building (which I had assumed the --keep-going flag prevented) Here's an example of yasm failing to build http://paste.lisp.org/display/318806