[Ada] Fix setting of Has_Predicate flag for aggregate subtypes

[Ada] Fix setting of Has_Predicate flag for aggregate subtypes

This patch enures that the subtype of an aggregate has the Has_Predicate
flag properly set if the array component has a predicate, including the
case the predicate function for the component has not been constructed
yet.

2018-12-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_aggr.adb (Array_Aggr_Subtype. Resolve_Aggr_Expr): Indicate
	that aggregate subtype has a predicate if the component type has
	a predicate; do not rely on exisatence of predicate function for
	component, in case component is a type no yet frozen, for which
	predicate function has not been created yet.

From-SVN: r267007