perl: synchronize changes done to 5.20 and 5.22

Some multiple-output changes were previously only in 5.22,
but since master is still using 5.20, let's stick with that version
on closure-size as well.
https://github.com/NixOS/nixpkgs/commit/741bf840dad05cd1728481045466811ae8ae8281#commitcomment-14784970