numpy: enable numpy.distutils patch only if it's also in distutils

[veprbl]

Motivation for this change

Fix a bug in #19585

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

Fixes: 095095c ('python: add C++ compiler support for distutils')
Cc: @FRidh

[mention-bot]

@veprbl, thanks for your PR! By analyzing the history of the files in this pull request, we identified @FRidh, @edolstra and @chaoflow to be potential reviewers.

[FRidh]

testing now