I ran across the exact failure I am seeing on a CPAN Testers post
No, this is a different failure in that it has a different cause. The CPAN testers failure you've quoted occurs because PERL_UNUSED_VAR is not defined in perl 5.6.1 (though it is defined for perls 5.8 and 5.10). This is not related to your particular problem.
Cheers, Rob
Comment on Re: Math::Pari make test fails on Pari.so
...that's good to know too. I think this is why I didn't catch on, I assumed it might be a more severe issue if one of the CPAN testers had made that post.