Fix testability of pkgs/stdenv/linux/default.nix
Fix testability of pkgs/stdenv/linux/default.nix

The point here is that it's always possible to debug this staging
logic by using `nix-repl pkgs/stdenv/linux'. The modular-stdenv
change introduced the lib dependency, which we now default to
../../../lib.

No derivation or out hashes of stdenvLinux is changed by this commit.

NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,triton/triton,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs