* The final installation was not at the correct place; looks like
the DESTDIR that worked previously needs to be PREFIX now.
* Make tests work. These aldo didn't run anymore even though it
looked they might've in the past.
For that, add a bunch of local Perl packages needed by these
tests that were not available in nixpkgs yet (Plan is to move
them to perl-packages.nix, but as first step have them local
here to have a self-contained z88dx.
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