Do not use duplocale if building for libnix because it isnt supported yet

cmake/config.h.in

@@ -137,6 +137,9 @@
 /* Define to 1 if you have the `uselocale' function. */
 #cmakedefine HAVE_USELOCALE
 
+/* Define to 1 if you have the `duplocale' function. */
+#cmakedefine HAVE_DUPLOCALE
+
 /* Define to 1 if newlocale() needs freelocale() called on it's `base` argument */
 #cmakedefine NEWLOCALE_NEEDS_FREELOCALE