[Ada] Error when passing subprogram'Access to null-defaulted formal subprogram

[Ada] Error when passing subprogram'Access to null-defaulted formal subprogram

gcc/ada/

	* freeze.adb (Freeze_Subprogram): Don't propagate conventions
	Intrinsic or Entry to anonymous access-to-subprogram types
	associated with subprograms having those conventions. Update
	related comment.
	* sem_attr.adb (Resolve_Attribute, Attribute_*Access): Remove
	special-case warning code for cases where a called subprogram
	has convention Intrinsic as well as its formal's type (the
	expected type for the Access attribute), since this case can no
	longer occur.