ada: Fix internal error on call with parameter of predicated subtype

The problem is that the predicated subtype does not inherit all the required
attributes of a string subtype with a static predicate.

gcc/ada/
	* sem_ch3.adb (Analyze_Subtype_Declaration): Remove a short-circuit
	for subtypes without aspects when it comes to predicates.
	* sem_util.adb (Inherit_Predicate_Flags): Deal with private subtypes
	whose full view is an Itype.