Define HAVE_STRNLEN correctly.

include/config-win.h:
  strnlen() presents in the build in library only starting from
  Visual Studio 2005, identified by _MSC_VER 1400.
  Previous versions of Visual Studio didn't have this
  function, so they need the MySQL replacement function to be compiled.

include/config-win.h

@@ -350,7 +350,10 @@ inline double ulonglong2double(ulonglong value)
 #define SPRINTF_RETURNS_INT
 #define HAVE_SETFILEPOINTER
 #define HAVE_VIO_READ_BUFF
+#if defined(_MSC_VER) && _MSC_VER >= 1400
+/* strnlen() appeared in Studio 2005 */
 #define HAVE_STRNLEN
+#endif
 #define HAVE_WINSOCK2
 
 #define strcasecmp stricmp