bug#35010: Many CPAN download URLs are no longer available

[Mark H Weaver <mhw@netris.org>]

Many perl packages cannot be built on hydra.gnu.org because the source
code is no longer available at the source URLs known to Guix.  Moreover,
apparently they were gone by the time Hydra made its first build
attempt.

Here are some examples:

  mirror://cpan/authors/id/E/ET/ETHER/URI-1.76.tar.gz
  mirror://cpan/authors/id/S/SY/SYOHEX/Mouse-v2.5.6.tar.gz
  mirror://cpan/authors/id/S/SZ/SZABGAB/Class-Date-1.1.17.tar.gz
  mirror://cpan/authors/id/S/SZ/SZABGAB/SVG-2.84.tar.gz
  mirror://cpan/authors/id/A/AB/ABW/Template-Toolkit-2.28.tar.gz
  mirror://cpan/authors/id/D/DA/DAGOLDEN/Log-Any-1.707.tar.gz
  mirror://cpan/authors/id/K/KE/KENTNL/Carp-Clan-6.07.tar.gz
  mirror://cpan/authors/id/R/RJ/RJBS/Carp-1.50.tar.gz
  mirror://cpan/authors/id/D/DA/DAGOLDEN/File-Temp-0.2309.tar.gz
  mirror://cpan/authors/id/M/MA/MAKAMAKA/Text-CSV-1.99.tar.gz

and these are the corresponding download derivations:

  /gnu/store/c73chq3k1z1n2wnbh0sbi2vwip6dfzbk-URI-1.76.tar.gz.drv
  /gnu/store/550r5gdrvs5370rsa2zwp1bs0xwj5dnm-Mouse-v2.5.6.tar.gz.drv
  /gnu/store/qxkgrj9gz1kp9id2d7d3mzrfn5b56019-Class-Date-1.1.17.tar.gz.drv
  /gnu/store/7239snjzan94plk58hw2zgachq71rh64-SVG-2.84.tar.gz.drv
  /gnu/store/qn1w1wvy5x2wngq4845j60i3qvkwhwvi-Template-Toolkit-2.28.tar.gz.drv
  /gnu/store/w1cb4r6c0v37xcjav6z16fzbc2zp47ff-Log-Any-1.707.tar.gz.drv
  /gnu/store/7gdg0aqsc3i7iwnrajcv6skkjbnf6z4r-Carp-Clan-6.07.tar.gz.drv
  /gnu/store/2b088r47jay82d91w62hr35lszqbdrkk-Carp-1.50.tar.gz.drv
  /gnu/store/jsddlzd5aba8vnjz1adggcxmvkgv5qf6-File-Temp-0.2309.tar.gz.drv
  /gnu/store/y2yb19kf1pfblhqwxcll7rrh6pgpr9sh-Text-CSV-1.99.tar.gz.drv

At least some, and probably most, of these URIs were updated quite
recently.  For example, the 'perl-mouse', 'perl-carp-clan', and
'perl-file-temp' were all updated on March 23, and presumably the source
URIs worked at that point, but then all three URIs had to be updated two
days later to fix the broken download links.

The CPAN download URLs that we are using are apparently not long-lived.
Does anyone know if CPAN, or perhaps another site, offers more stable
download URIs for these packages?

      Thanks,
        Mark