nix.systemFeatures: minor fix
nix.systemFeatures: minor fix

following up #59148
I forgot the default case of the architectures which do not have minor brothers whose code they can run ("westmere" or any of of AMD)
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs