gem-config: patch getconf path in prometheus-client-mmap

    meta.mainProgram = "rbprettier";

  };

  prometheus-client-mmap = attrs: {

    dontBuild = false;

    postPatch = let

      getconf = if stdenv.hostPlatform.isGnu then stdenv.cc.libc else getconf;

    in ''

      substituteInPlace lib/prometheus/client/page_size.rb --replace "getconf" "${lib.getBin getconf}/bin/getconf"

    '';

  };

  glib2 = attrs: {

    nativeBuildInputs = [ pkg-config ]

      ++ lib.optionals stdenv.isDarwin [ DarwinTools ];