made all XPM const to avoid warnings from mingw32 4.0 and adopt the code accordingly (patch 1872384)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51228 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/widgets/itemcontainer.h

@@ -25,7 +25,7 @@ class ItemContainerWidgetsPage : public WidgetsPage
 public:
     ItemContainerWidgetsPage(WidgetsBookCtrl *book,
                              wxImageList *image_list,
-                             char* icon[]);
+                             const char *const icon[]);
     virtual ~ItemContainerWidgetsPage();
 
     void OnButtonTestItemContainer(wxCommandEvent& event);