bug#23077: Perl's closure is too big

[Thompson, David]

If you run 'guix size perl' you will notice that, as of this writing,
138.2MiB of Perls' 307.6MiB closure is due to referencing gcc's
default output in '/lib/perl5/5.22.1/x86_64-linux/Config_heavy.pl'.
Perl's large closure inflates the closures of many other packages,
such as openssl.

Does anyone familiar with Perl know if we really need to a reference
to GCC here?  Would be great to remove it. :)

- Dave