[20.09] Added mime info path for mimemagic

[nixy]

Motivation for this change

The fixes done to make mimemagic continue to work with Nix should be backported to the current stable version since there is currently no version of mimemagic available that can be built without these fixes.

Original commits/discussion in #117702

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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.

[SuperSandro2000]

This is a semi-automatic executed nixpkgs-review with nixpkgs-review-checks extension. It is checked by a human on a best effort basis and does not build all packages (e.g. lumo, tensorflow or pytorch).
If you have any questions or problems please reach out to SuperSandro2000 on IRC.

Result of nixpkgs-review pr 119757 run on x86_64-linux 1

1 package marked as broken and skipped:

• frab

4 packages built:

• gitlab
• gitlab-ee
• iruby
• redmine

[SuperSandro2000]

Please follow the contributing guide when backporting commits.

[nixy]

Please follow the contributing guide when backporting commits.

I am unsure what changes are being requested here. I made a best effort attempt at following the contributing guidelines here and if I have made some mistake it isn't obvious to me. Happy to make any changes but not sure what needs to be done here.

[SuperSandro2000]

The important part for this PR is https://github.com/NixOS/nixpkgs/blob/master/.github/CONTRIBUTING.md#backporting-changes and especially the git cherry-pick -x part.

[aanderse]

This is needed to resolve #120413, so this indirectly becomes a "security" tag.

ping @SuperSandro2000 please ❤️

[aanderse]

Thanks!