[Bug-gnuzilla] Up-to-date IceCat source tarballs now available via GNU Guix

[Mark H Weaver]

GNU Guix is now capable of producing up-to-date source tarballs for
IceCat that should hopefully build on any system that IceCat supports.

For example, GNU Guix has icecat-60.7.2-guix1, which includes fixes for
CVE-2019-11707 and CVE-2019-11708, which are apparently quite serious
flaws that are being actively exploited in the wild.

The IceCat source tarballs produced by GNU Guix are almost identical to
the official IceCat tarballs, except that the timestamps and file
ordering in the tarball are canonicalized, and a few manifest files
within the tarball are sorted differently.

After installing Guix <https://gnu.org/s/guix>, the command to produce
the IceCat tarball is:

  guix build --source icecat

      Mark