rustc: link libc++abi on Darwin

[reckenrode]

Description of changes

Fixes the build failure on staging-next. See #241951 (comment).

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.11 Release Notes (or backporting 23.05 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.

[reckenrode]

I’ve built this with a clang 16 stdenv, but there’s no reason it shouldn’t work with a clang 11 one.

[tjni]

This LGTM.

I wasn't able to find on Hydra an obvious error message. Would you mind adding what it was here for future reference?

[reckenrode]

I wasn't able to find on Hydra an obvious error message. Would you mind adding what it was here for future reference?

Sorry about that. I was mistaken re: Hydra. The failures were timeouts. I encountered an error with missing symbols due to libc++abi and assumed that was the issue. I’ll be more careful about making assumptions in the future.

I did try to reproduce the failure to get a stack trace, but now I can’t reproduce it with clang 11. It must have been an issue when using clang 16. 😑