Fix wxMSW build in UTF-8 build.

Need an explicit cast to convert the buffer returned by wxString::t_str() to a
pointer in this case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77942 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/calctrl.cpp

@@ -108,7 +108,7 @@ wxCalendarCtrl::Create(wxWindow *parent,
     }
 
     const wxChar * const clsname = s_clsMonthCal.IsRegistered()
-        ? s_clsMonthCal.GetName().t_str()
+        ? static_cast<const wxChar*>(s_clsMonthCal.GetName().t_str())
         : MONTHCAL_CLASS;
 
     if ( !MSWCreateControl(clsname, wxEmptyString, pos, size) )