Define HAVE_UCOL_STRCOLLUTF8 on Windows

This should normally be determined by a configure check, but until
someone figures out how to do that on Windows, it's better that the code
uses the new function by default.

src/include/pg_config.h.win32

@@ -457,6 +457,9 @@
 /* Define to 1 if you have the external array `tzname'. */
 /* #undef HAVE_TZNAME */
 
+/* Define to 1 if you have the `ucol_strcollUTF8' function. */
+#define HAVE_UCOL_STRCOLLUTF8 1
+
 /* Define to 1 if the system has the type `uint64'. */
 /* #undef HAVE_UINT64 */