How do I express a dependency on a Perl version?

[A. Pagaltzis]

Hi all,

I have a module that I don’t want to spend the effort to make it
work in Perl versions earlier than 5.8. Got no Unicode support?
You lose.

But how do I say this in the Build.PL?

Regards,
-- 
Aristotle Pagaltzis // <http://plasmasturm.org/>