gcc8 is failing on x86_64-darwin:

Job: https://hydra.nixos.org/job/nixpkgs/trunk/gcc8.x86_64-darwin

Not sure what's going on. Clang gives this error:

clang-5.0: error: unsupported option '--gstabs'