clang: don't set machine flags for overridden target

[alyssais]

Description of changes

We already did this for -march in 12b0e8a ("clang: don't set -march for overridden target"), but it should have been done for all machine flags, for the same reason.

Example bug this fixes:

nix-shell -E '
  with import ./. {
    crossSystem = {
      system = "powerpc64le-linux";
      gcc.cpu = "power10";
    };
  };
  clangStdenv.mkDerivation { name = "test"; }
' --run '$CC -target wasm32-unknown-unknown -c /dev/null'

Which previously failed with:

  clang: error: unsupported option '-mcpu=' for target 'wasm32-unknown-unknown'

@vcunat could you please test whether this fixes rustc on aarch64-darwin, as reported in #309580 (comment)? If it does, we can make a temporary fix on staging-next.

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/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 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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[Samasaur1]

The Swift change (paralleling #301103) looks right to me, but I'm building it and a Swift package just to make sure everything works out

[vcunat]

rustc built for me on this PR's commit on aarch64-darwin (the whitespace change doesn't cause rebuild).

[Samasaur1]

My Swift package builds and runs. LGTM

[vcunat]

If it does, we can make a temporary fix on staging-next.

@alyssais are you working on that?

[alyssais]

Should have it done later today.

[alyssais]

#318447

[Mic92]

Passes my eye-ball test, didn't test it.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/is-there-a-way-to-install-a-macos-pkg-from-an-url/49660/10