[Ada] Handle correctly current instance of PO in local subprogram Global

[Ada] Handle correctly current instance of PO in local subprogram Global

gcc/ada/

	* sem_prag.adb (Analyze_Global_Item): Handle specially the
	current instance of a PO.
	* sem_util.ads (Is_Effectively_Volatile,
	Is_Effectively_Volatile_For_Reading): Add parameter
	Ignore_Protected.
	* sem_util.adb (Is_Effectively_Volatile,
	Is_Effectively_Volatile_For_Reading): Add parameter
	Ignore_Protected to compute the query results ignoring protected
	objects/types.
	(Is_Effectively_Volatile_Object,
	Is_Effectively_Volatile_Object_For_Reading): Adapt to new
	signature.