commit f79998e970bc6484d0d99c37e5cad179d76e0190
Author: Philippe Makowski <pmakowski@espelida.com>
Date:   Sun Jul 3 17:49:47 2016 +0200

    dont-duplicate-flags-in-sysconfig

diff --git a/Lib/distutils/sysconfig.py b/Lib/distutils/sysconfig.py
index 6e58533..a4846eb 100644
--- a/Lib/distutils/sysconfig.py
+++ b/Lib/distutils/sysconfig.py
@@ -357,7 +357,10 @@ def parse_makefile(fn, g=None):
                     done[n] = item = ""
                 if found:
                     after = value[m.end():]
-                    value = value[:m.start()] + item + after
+                    value = value[:m.start()]
+                    if item.strip() not in value:
+                        value += item
+                    value += after
                     if "$" in after:
                         notdone[name] = value
                     else:
diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index 31bc2ed..b021cce 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -294,7 +294,10 @@ def _parse_makefile(filename, vars=None):
 
                 if found:
                     after = value[m.end():]
-                    value = value[:m.start()] + item + after
+                    value = value[:m.start()]
+                    if item.strip() not in value:
+                        value += item
+                    value += after
                     if "$" in after:
                         notdone[name] = value
                     else: