HPUX 11.11 does not support -z flag to tar

HPUX 11.11 (and others?) need to use gzip to manage compressed tar (tgz) files, as their version of tar does not support -z.

Not certain if there is anything else that needs to be done from a build perspective (not familiar with fatpack, dz, etc).  There should probably be some more specific platform selection, but I don't have access to newer versions of HP-UX.