Hi,

I'm attaching the patch. It builds in 'master', but I can't test it in
'core-updates'.

(Note that some tweaking is required to apply it in 'master'.)

# ./bootstrap
# ./configure --with-nixpkgs=/home/nixpkgs-github --localstatedir=/nix/var
# make
# nix-worker --daemon &
# ./pre-inst-env guix-build -K coreutils

[...]

starting download of `/nix/store/yhgwc596bny14wh6567pwsxj7lrcypiy-binutils-2.22.tar.bz2' from `http://ftpmirror.gnu.org/binutils/binutils-2.22.tar.bz2'...
ERROR: In procedure getaddrinfo: Name or service not known

[...]

error: build failed: build of `/nix/store/14l27j4hmzlpzfbmkw298bddg73v64di-coreutils-8.20.drv' failed

# wget --spider http://ftpmirror.gnu.org/binutils/binutils-2.22.tar.bz2

[...]

Remote file exists.

Nikita