Make wxVSCROLL explicitly of int type.

Its value (0x80000000) is outside of the int type range on 32 bit platforms,
but we still want to allow using it as an initializer of int and/or long
variables for consistency with the other types, so cast it to int explicitly
to suppress -Wnarrowing warnings from recent g++ which were given when doing
this before.

include/wx/defs.h

@@ -1779,7 +1779,12 @@ enum wxBorder
 /*
  * Window (Frame/dialog/subwindow/panel item) style flags
  */
-#define wxVSCROLL               0x80000000
+
+/* The cast is needed to avoid g++ -Wnarrowing warnings when initializing
+ * values of int type with wxVSCROLL on 32 bit platforms, where its value is
+ * greater than INT_MAX.
+ */
+#define wxVSCROLL               ((int)0x80000000)
 #define wxHSCROLL               0x40000000
 #define wxCAPTION               0x20000000