[staging-next] python3Packages.libarcus: fix build against protobuf 3.18+

[r-burns]

Still needs upstream resolution (Ultimaker/libArcus#121), but we can grab a Void Linux Vcpkg patch in the meantime

Motivation for this change

For #138268

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all packages 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/)
• 21.11 Release Notes (or backporting 21.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[r-burns]

Result of nixpkgs-review pr 138565 run on x86_64-linux 1

6 packages built:

• cura
• curaengine
• python38Packages.libarcus
• python38Packages.uranium
• python39Packages.libarcus
• python39Packages.uranium

[gebner]

Removing the return in the error case looks a bit fishy to me, but as long as it works I'm happy. Did you try cura?

[r-burns]

Hmm you're right, that is kind of suspicious. I haven't tried running any dependencies but that seems like a good idea.

[r-burns]

@gebner I found a more surgical patch on Vcpkg. Built cura, not sure what to test though.

[lukegb]

I'm going to merge this as is; the patch looks good, so if cura builds then let's roll with it.