darwin.binutils: properly handle cctools-llvm

[reckenrode]

Description of changes

• Only link libexec when using cctools-port. cctools-llvm does not have a libexec folder;
• Use as provided by cctools-llvm, which is already using the clang-integrated assembler on both platforms; and
• Clean up inconsistent use of builtins.

This was reported on Matrix. libexec is a dangling symlink, which prevents binutils from being added to home.packages after upgrading to 23.11 with the following error:

darwin-rebuild --flake ~/path-to-flake/ build
building the system configuration...
error: builder for '/nix/store/77pb55j08rfh3lbxxx5v1q7nyih900d3-home-manager-path.drv' failed with exit code 2;
       last 1 log lines:
       > error: not a directory: `/nix/store/8kkn9qqg1mnny41cc8i33ws9ilmxyww1-cctools-binutils-darwin-16.0.6-973.0.1/libexec'
       For full logs, run 'nix log /nix/store/77pb55j08rfh3lbxxx5v1q7nyih900d3-home-manager-path.drv'.
error: 1 dependencies of derivation '/nix/store/cg4axwsiaygf47xa472h50nrp3nl9fm4-home-manager-generation.drv' failed to build
error: 1 dependencies of derivation '/nix/store/pghcqfradm590s6yvri7n8p1iykal267-user-environment.drv' failed to build
error: 1 dependencies of derivation '/nix/store/9dnqxmm927zl3mzcfd2a15cmx9wxn6bz-activation-brendan.drv' failed to build
error: 1 dependencies of derivation '/nix/store/30rpflszvj9js6v6isnfxjr9asg39f5l-darwin-system-23.11.20240317.614b461+darwin4.bcc8afd.drv' failed to build

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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[reckenrode]

Adding the backport-staging-23.11 label because this was reported against 23.11.

[ghost]

change seems fine. nested optionalStrings is unfortunate.

looking over the comments it seems like some of these steps are outdated. not being able to handle movq %rbp, %xmm0 is just weird.

[github-actions]

Successfully created backport PR for staging-23.11:

• [Backport staging-23.11] darwin.binutils: properly handle cctools-llvm #299582