Avoid test failures with Strawberry Perl

Automated tests showed link failures under Strawberry Perl. This should have
been caught in Makefile.PL, but it looks like wasn't because `-lz`
succeeded. So, make sure we succeed in linking with at least something
resembling an OpenSSL library before writing Makefile.

It is entirely possible that I have misdiagnosed the issue but this is my
best guess at the moment.