release-cross: replace x86_64-darwin with aarch64-darwin

[szlend]

I propose trading x86_64-darwin for aarch64-darwin as the main darwin cross-compiling build platform. ARM Macs have been introduced in 2020 and the last Intel MacBooks have been discontinued in 2023 so I think most people would find aarch64-darwin more useful here.

See #284465

I guess the main question here is whether the aarch64-darwin builders are numerous enough to support this without slowing down native builds too much (relative to x86_64-darwin).

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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.

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[szlend]

I guess the main question here is whether the aarch64-darwin builders are numerous enough to support this without slowing down native builds too much (relative to x86_64-darwin).

From Matrix:

Winter: x86_64-darwin = aarch64-darwin with Rosetta for the sake of our infra

So this would actually put some load off of darwin builders, which is a nice side benefit.

[dwt]

This looks lovely, as it would make cross compilation from arm-darwin much faster.

[dwt]

How about the documentation of Nixpkgs? I know of that thing, but there are probably more places?