perl: fix errant references when cross-compiling

[lopsided98]

Motivation for this change

Cross-compiled Perl ends up with references to its source tarball and build coreutils.

Things done

The source tarball reference was a bit perplexing, but it turns out that Perl's build system uses the src environment variable, and writes its value into a header in the output. For native builds, some part of the config ends up of overwriting this variable, but this does not happen when cross-compiling.

The coreutils reference was simply an assumption that the correct binary would be in PATH.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @edolstra

[lopsided98]

I guess we need some special case for the Darwin bootstrap perl. I'm not sure what package provides pwd in that case.

[lopsided98]

Oh, I see #58979 ran into the same problem.

[lopsided98]

I applied the coreutils fix only to cross builds and added a comment explaining why this was done.

[lopsided98]

Sorry, I accidentally rebased on master...

[Ericson2314]

I would put the comments outside the ''...'' that way they don't affect the drv. Otherwise looks good!

[lopsided98]

I fixed the comments.

[Ericson2314]

Thank you!