Cygwin defines this since 1.7.8, but our wchar_t is only 16-bit while
this code seems to assume 32-bit wchar_t.  So, either some incorrect
assumptions need to be fixed in the __STDC_ISO_10646__ code paths, or
the conditionals need to also be guarded && (__SIZEOF_WCHAR_T__ == 4).

Reported by SLao:
http://article.gmane.org/gmane.os.cygwin.ports.general/1330

--- origsrc/glib-2.36.4/glib/gunicollate.c	2013-05-07 13:26:07.000000000 -0500
+++ src/glib-2.36.4/glib/gunicollate.c	2013-11-30 21:36:27.710188300 -0600
@@ -37,9 +37,12 @@
 #include "gstrfuncs.h"
 #include "gtestutils.h"
 #include "gcharset.h"
-#ifndef __STDC_ISO_10646__
+#if !defined(__STDC_ISO_10646__) || defined(G_WITH_CYGWIN)
 #include "gconvert.h"
 #endif
+#ifdef G_WITH_CYGWIN
+#undef __STDC_ISO_10646__
+#endif
 
 
 #ifdef _MSC_VER