core/pkgs/by-name/pk/pkg-config/packages.nix

{ ... }:
res: pkgs: super:

with pkgs; {
  pkg-config-unwrapped = callPackage ./. { };

  pkg-configUpstream = lowPrio (pkg-config.override
    (old: { pkg-config = old.pkg-config.override { vanilla = true; }; }));

  pkg-config = callPackage (path + "/pkgs/build-support/pkg-config-wrapper") {
    pkg-config = pkg-config-unwrapped;
  };
}