ada: Set Is_Not_Self_Hidden flag in more cases

ada: Set Is_Not_Self_Hidden flag in more cases

More work-in-progress for changing E_Void checks to the flag.

gcc/ada/

	* sem_ch9.adb (Analyze_Protected_Type_Declaration): Set the flag
	for protected types.
	(Analyze_Single_Protected_Declaration): Likewise, for singleton
	protected objects.
	(Analyze_Task_Type_Declaration): Set the flag for task types.
	(Analyze_Single_Task_Declaration): Likewise, for singleton task
	objects.
	* sem_ch10.adb (Decorate_Type): Set the flag for types treated as
	incomplete.
	(Build_Shadow_Entity): Set the flag for shadow entities.
	(Decorate_State): Set the flag for an abstract state.
	(Build_Limited_Views): Set the flag for limited view of package.
	* sem_attr.adb (Check_Not_Incomplete_Type): Disable the check when
	this is a current instance.