Suppress unavoidable -Wsuggest-override in wxCompositeWindow

This allows new wxMSW wxRadioBox implementation to use wxCompositeWindow
without triggering this warning due to the base wxStaticBox class
already inheriting from wxCompositeWindow too.

include/wx/compositewin.h

@@ -132,10 +132,24 @@ protected:
     }
 
 private:
+    // It may happen that we the base class W already is a wxCompositeWindow
+    // and so already has GetCompositeWindowParts(). This actually works fine,
+    // as it just gets overridden by the most derived class, but triggers a
+    // warning, so disable this warning explicitly as we can't do anything else
+    // about it here (as actually using "override" here would result in an
+    // error for the first class in the hierarchy using wxCompositeWindow).
+#if wxCHECK_GCC_VERSION(5,1)
+    wxGCC_ONLY_WARNING_SUPPRESS(suggest-override)
+#endif
+
     // Must be implemented by the derived class to return all children to which
     // the public methods we override should forward to.
     virtual wxWindowList GetCompositeWindowParts() const = 0;
 
+#if wxCHECK_GCC_VERSION(5,1)
+    wxGCC_ONLY_WARNING_RESTORE(suggest-override)
+#endif
+
     template <class T, class TArg, class R>
     void SetForAllParts(R (wxWindowBase::*func)(TArg), T arg)
     {