I don't think this information is provided or maintained. There was a moment, I thought you can send some feedback to cpan on this, but then I realized it is not realistic. As most of those modules are maintained by persons like you and me, I would doubt they have the effort/environment to test all this.
I think it is really in everyone's hands to try it by yourself.
One thing you can suggest is for CPAN to maintain certain info like compatibility etc., not by author, but by users. For example, if you used module A::B::C, with perl n.n.n on platform XYZ, then you should be allowed to go CPAN, and certify this, so other users have a similar environment can be benefited from your experience.
Update:
Checked
pfaut's link, Hm... coverage is not good enough. They don't have a single tester using AIX, I will join. If you can help, pls join.