libfixposix: 30b75609 -> 0.4.1

[orivej]

Motivation for this change

Nothing in nixpkgs depends on this library, the update is needed for use with iolib

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
  • macOS
  • 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.

[mention-bot]

@orivej, thanks for your PR! By analyzing the history of the files in this pull request, we identified @7c6f434c, @joachifm and @dezgeg to be potential reviewers.