gnuplot-qt: fix wrapper

  CXXFLAGS = lib.optionalString (stdenv.isDarwin && withQt) "-std=c++11";

  # we'll wrap things ourselves

  dontWrapGApps = true;

  dontWrapQtApps = true;

  # binary wrappers don't support --run

  postInstall = lib.optionalString withX ''

    wrapProgram $out/bin/gnuplot \

    wrapProgramShell $out/bin/gnuplot \

       --prefix PATH : '${gnused}/bin' \

       --prefix PATH : '${coreutils}/bin' \

       --prefix PATH : '${fontconfig.bin}/bin' \

       "''${gappsWrapperArgs[@]}" \

       "''${qtWrapperArgs[@]}" \

       --run '. ${./set-gdfontpath-from-fontconfig.sh}'

  '';