Qt::ApplicationInactive breaks compilation

[Pavel Sanda]

Hi Stephan,

I can't compilet any longer on older Qt:
  CXX      GuiApplication.o
GuiApplication.cpp:1015:6: error: 'ApplicationState' in namespace 'Qt' does not 
name a type              
  Qt::ApplicationState last_state_;
      ^                  
GuiApplication.cpp: In constructor 'lyx::frontend::GuiApplication::Private::Priv
ate()':                  
GuiApplication.cpp:947:29: error: class 'lyx::frontend::GuiApplication::Private'
 does not have any field named 'last_state_'
   global_menubar_(nullptr), last_state_(Qt::ApplicationInactive)
                             ^
GuiApplication.cpp:947:41: error: 'ApplicationInactive' is not a member of 'Qt'
   global_menubar_(nullptr), last_state_(Qt::ApplicationInactive)

Could you ifdef last_state_ in the same way ytou do it with connect?

Thanks,
Pavel