Code clean in Tab.cpp and Fixed couple of Mac-warnings in :

GUI.cpp
GUI_App.cpp
GUI_ObjectList.cpp
MainFrame.hpp
Plater.cpp
PresetBundle.cpp
PresetHints.cpp
Tab.cpp
Tab.hpp
wxExtensions.cpp
wxExtensions.hpp

src/slic3r/GUI/Tab.hpp

@@ -321,7 +321,6 @@ protected:
 
 class TabPrint : public Tab
 {
-    bool is_msg_dlg_already_exist {false};
 public:
 	TabPrint(wxNotebook* parent) : 
 // 		Tab(parent, _(L("Print Settings")), L("print")) {}