[21.05] libgudev: support cross-compilation by disabling introspection and vala

[erdnaxe]

Motivation for this change

Original pull request: #123936

This enables to cross-compile NixOS stable for aarch64.

With this patch I was able to build NixOS stable for my aarch64 board and it is working great.

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/)
• 21.11 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.

[Mic92]

Not sure how far we are from supporting introspection: cc @Ericson2314 in #88222

[Mindavi]

Not sure if we should backport that all into the release even if that is resolved shortly. Since upstream is not that responsive, I don't have high hopes that it'll happen soon.

Even if they (gobject-introspection upstream) merge the PR, there's still some work to do to get it actually working (I think there was a draft PR for meson too?). At least, some integration will still be required. I don't think it will happen very soon.

[Mindavi]

In my opinion, this is good to go.