matplotlib: Don't search in global paths

Sets the `basedirlist` option in setup.cfg such that distutils does not search
for headers and libraries in `/usr`, and `/usr/local`.

Otherwise the build can fail on non-NixOS machines, see #15993.

pkgs/development/python-modules/matplotlib/basedirlist.patch

@@ -0,0 +1,8 @@
+diff --git a/setup.cfg b/setup.cfg
+new file mode 100644
+index 0000000..6f81985
+--- /dev/null
++++ b/setup.cfg
+@@ -0,0 +1,2 @@
++[directories]
++basedirlist = .

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

@@ -35,7 +35,9 @@ buildPythonPackage rec {
     ++ stdenv.lib.optional enableGtk2 pygtk
     ++ stdenv.lib.optionals enableGtk3 [ cairo pycairo gtk3 gobjectIntrospection pygobject3 ];
 
-  patches = stdenv.lib.optionals stdenv.isDarwin [ ./darwin-stdenv.patch ];
+  patches =
+    [ ./basedirlist.patch ] ++
+    stdenv.lib.optionals stdenv.isDarwin [ ./darwin-stdenv.patch ];
 
   checkPhase = ''
     ${python.interpreter} tests.py