[Ada] Spurious error on Old attribute reference in delta aggregate

[Ada] Spurious error on Old attribute reference in delta aggregate

gcc/ada/

	* sem_aggr.adb (Resolve_Delta_Array_Aggregate): For an
	association that is an iterated component association, attach
	the copy of the expression to the tree prior to analysis, in
	order to preserve its context. This is needed when verifying
	static semantic rules that depend on context, for example that a
	use of 'Old appears only within a postcondition.