python.pkgs.matplotlib: use pkgs.pkgconfig

pkgs/development/python-modules/matplotlib/default.nix

@@ -35,13 +35,15 @@ buildPythonPackage rec {
 
   XDG_RUNTIME_DIR = "/tmp";
 
+  nativeBuildInputs = [ pkgconfig ];
+
   buildInputs = [ python which sphinx stdenv ]
     ++ stdenv.lib.optional enableGhostscript ghostscript
     ++ stdenv.lib.optional stdenv.isDarwin [ Cocoa ];
 
   propagatedBuildInputs =
     [ cycler dateutil nose numpy pyparsing tornado freetype kiwisolver
-      libpng pkgconfig mock pytz ]
+      libpng mock pytz ]
     ++ stdenv.lib.optional (pythonOlder "3.3") backports_functools_lru_cache
     ++ stdenv.lib.optional enableGtk2 pygtk
     ++ stdenv.lib.optionals enableGtk3 [ cairo pycairo gtk3 gobject-introspection pygobject3 ]

pkgs/top-level/python-packages.nix

@@ -2997,6 +2997,7 @@ in {
   in callPackage path {
     stdenv = if stdenv.isDarwin then pkgs.clangStdenv else pkgs.stdenv;
     inherit (pkgs.darwin.apple_sdk.frameworks) Cocoa;
+    inherit (pkgs) pkgconfig;
   };
 
   matrix-client = callPackage ../development/python-modules/matrix-client { };