emacs: darwin: use architecture-native SDK

[tnytown]

Description of changes

#253892 bumped the Emacs derivations to apple_sdk_11_0 for headers required by the Mac port on Apple Silicon Macs. That change caused many issues on older macOS versions. This change switches back to the platform-native SDK (10.12 on x86_64-darwin and 11.0 on aarch64-darwin) and gates the newly required headers by architecture.

CC @quentinmit and @knl. I tested emacs-macport for x86_64-darwin and the problematic aligned_alloc isn't being imported anymore, but I would appreciate confirmation from your end.

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/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 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.

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[AndersonTorres]

??

[tnytown]

Ouch, did this by accident while cleaning up my GitHub forks. @AndersonTorres would you be interested in this change if I re-submit it? I hadn't realized that it's been stalled all this time.