Issue #3696: Error parsing arguments on OpenBSD <= 4.4 and Cygwin.

Patch by Amaury Forgeot d'Arc, reviewed by me.
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 4a10db6..85f7e37 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -803,6 +803,10 @@
 /* Define to 1 if you have the `wcsxfrm' function. */
 #undef HAVE_WCSXFRM
 
+/* Define if mbstowcs(NULL, "text", 0) does not return the number of 
+   wide chars that would be converted */
+#undef HAVE_BROKEN_MBSTOWCS
+
 /* Define if tzset() actually switches the local timezone in a meaningful way.
    */
 #undef HAVE_WORKING_TZSET