fix (harmless for now) g++ warning about non-virtual dtor

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58733 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/persist.h

@@ -136,6 +136,10 @@ private:
         m_doRestore = true;
     }
 
+    // trivial but virtual dtor
+    virtual ~wxPersistenceManager();
+
+
     // helpers of Save/Restore()
     //
     // TODO: make this customizable by allowing

src/common/persist.cpp

@@ -40,6 +40,10 @@ wxPersistenceManager& wxPersistenceManager::Get()
     return s_manager;
 }
 
+wxPersistenceManager::~wxPersistenceManager()
+{
+}
+
 wxString
 wxPersistenceManager::GetKey(const wxPersistentObject& who,
                              const wxString& name) const