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

From 08d26a80859023963bc2ffb41a0b6aed942685a9 Mon Sep 17 00:00:00 2001
From: Mike Frysinger <vapier@chromium.org>
Date: Fri, 15 May 2015 03:36:45 -0400
Subject: [PATCH 1/3] setupext: respect $PKG_CONFIG

When cross-compiling, it is common to set the PKG_CONFIG env var to a
custom pkg-config that knows about the target.  Make sure we respect
that just like the standard pkg-config tools suggest (pkg.m4).  If it
isn't set, we use the same default as today -- "pkg-config".
---
 setupext.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/setupext.py b/setupext.py
index 80b2a6c..29cddf9 100755
--- a/setupext.py
+++ b/setupext.py
@@ -253,7 +253,8 @@ class PkgConfig(object):
             self.has_pkgconfig = False
         else:
             self.set_pkgconfig_path()
-            status, output = getstatusoutput("pkg-config --help")
+            self.pkgconfig = os.environ.get('PKG_CONFIG', 'pkg-config')
+            status, output = getstatusoutput("%s --help" % self.pkgconfig)
             self.has_pkgconfig = (status == 0)
             if not self.has_pkgconfig:
                 print("IMPORTANT WARNING:")
@@ -286,7 +287,7 @@ class PkgConfig(object):
 
         executable = alt_exec
         if self.has_pkgconfig:
-            executable = 'pkg-config {0}'.format(package)
+            executable = '%s %s' % (self.pkgconfig, package)
 
         use_defaults = True
 
@@ -330,7 +331,7 @@ class PkgConfig(object):
             return None
 
         status, output = getstatusoutput(
-            "pkg-config %s --modversion" % (package))
+            '%s %s --modversion' % (self.pkgconfig, package))
         if status == 0:
             return output
         return None
-- 
2.4.0