bug#23682: can't create 32 bit guix container under a 64 bit GuixSD system

[Ander GM]

I can't create a 32 bit Guix container, once I setup the container as
it follows:

    $ guix environment -N --system=i686-linx --container --ad-hoc
    gcc-toolchain@4.9.3 findutils file coreutils sdl2 nano cang yasm
    mesa mesa-headers bash -- bash

    $ gcc  -dumpmachine

 returns 

    x86_64-unknown-linux-gnu instead of i686 .