https://github.com/matplotlib/matplotlib/pull/4430

From 3761303016cab0542891374032eca87e74d585bf Mon Sep 17 00:00:00 2001
From: Mike Frysinger <vapier@chromium.org>
Date: Fri, 15 May 2015 03:43:17 -0400
Subject: [PATCH 2/3] setupext: do not mess with PKG_CONFIG_PATH

The current code always sets PKG_CONFIG_PATH to build paths in / which
breaks cross-compiling -- things like /usr/lib are for the build system
(e.g. x86) and not for the target (e.g. arm).  Since we're adding paths
that are already the default for pkg-config, there's no point in trying
to be smart here.  Just punt the code.

This basically reverts commit 101beb975d3a1218350f02bf68dc2a43ac8ff148.
---
 setupext.py | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/setupext.py b/setupext.py
index 29cddf9..57d80e7 100755
--- a/setupext.py
+++ b/setupext.py
@@ -252,7 +252,6 @@ class PkgConfig(object):
         if sys.platform == 'win32':
             self.has_pkgconfig = False
         else:
-            self.set_pkgconfig_path()
             self.pkgconfig = os.environ.get('PKG_CONFIG', 'pkg-config')
             status, output = getstatusoutput("%s --help" % self.pkgconfig)
             self.has_pkgconfig = (status == 0)
@@ -262,20 +261,6 @@ class PkgConfig(object):
                     "    pkg-config is not installed.\n"
                     "    matplotlib may not be able to find some of its dependencies")
 
-    def set_pkgconfig_path(self):
-        pkgconfig_path = sysconfig.get_config_var('LIBDIR')
-        if pkgconfig_path is None:
-            return
-
-        pkgconfig_path = os.path.join(pkgconfig_path, 'pkgconfig')
-        if not os.path.isdir(pkgconfig_path):
-            return
-
-        try:
-            os.environ['PKG_CONFIG_PATH'] += ':' + pkgconfig_path
-        except KeyError:
-            os.environ['PKG_CONFIG_PATH'] = pkgconfig_path
-
     def setup_extension(self, ext, package, default_include_dirs=[],
                         default_library_dirs=[], default_libraries=[],
                         alt_exec=None):
-- 
2.4.0