The gnu.tar.gz contains a base GNU tarball that was generated using
crosshurd, but using it is discouraged, since it's probably outdated.

If you use Debian, or know how to install a temporary Debian chroot,
I suggest you use Debian's crosshurd package to generate an up-to-date
GNU installation in your local partition.

See http://packages.debian.org/unstable/misc/crosshurd.html

.