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/widgets.h

@@ -92,7 +92,7 @@ class WidgetsPage : public wxPanel
 public:
     WidgetsPage(WidgetsBookCtrl *book,
                 wxImageList *imaglist,
-                char* icon[]);
+                const char *const icon[]);
 
     // return the control shown by this page
     virtual wxControl *GetWidget() const = 0;