Use enum for wxMouseEvent::m_wheelAxis instead of int.

This variable can take only 2 values, use symbolic names for them instead of
difficult to understand 0 and 1.

See ##14105.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70961 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/carbon/nonownedwnd.cpp

@@ -547,7 +547,7 @@ WXDLLEXPORT void SetupMouseEvent( wxMouseEvent &wxevent , wxMacCarbonEvent &cEve
             wxevent.m_wheelDelta = 1;
             wxevent.m_linesPerAction = 1;
             if ( axis == kEventMouseWheelAxisX )
-                wxevent.m_wheelAxis = 1;
+                wxevent.m_wheelAxis = wxMOUSE_WHEEL_HORIZONTAL;
         }
         break ;