bug#14851: linux-libre-3.3.8-gnu disappeared

[Ludovic Courtès]

I’ve asked ftp-upload@ if they could allow me to upload linux-libre
tarballs to ftp.gnu.org.

In the meantime, I’ve uploaded this tarball to
ftp://alpha.gnu.org/gnu/guix/mirror and changed linux.scm to refer to it.

Thanks,
Ludo’.