perl: support cpan versions of core modules

Most of perl core modules are dual-life modules which exists on CPAN
as well as they do in perl core. Sometime, fixes are uploaded to CPAN
before a new perl is released which contains the fix of the core
module. Also, some modules recent releases aren't fully backported
to earlier releases (out of support, lack of specific feature, ...),
which makes it up to the distribution build to choose between core
or CPAN version, respectively.

Signed-off-by: Jens Rehsack <sno@netbsd.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>