ada: Error on instantiation of generic containing legal container aggregate

ada: Error on instantiation of generic containing legal container aggregate

When a container aggregate for a predefined container type (such as
a Vector type) that has an iterated component association occurs within
a generic unit and that generic is instantiated, the compiler reports
a spurious error message "iterated component association can only appear
in an array aggregate" and the compilation aborts (because Unrecoverable_Error
is raised unconditionally after that error). The problem is that as part of
the instantiation process, for aggregates whose type has a partial view,
in Copy_Generic_Node the compiler switches the visibility so that the full
view of the type is available, and for a type whose full view is a record
type this leads to incorrectly trying to process the aggregate as a record
aggregate in Resolve_Aggregate (making a call to Resolve_Record_Aggregate).

Rather than trying to address this by changing what Copy_Generic_Node does,
this can be fixed by reordering and adjusting the code in Resolve_Aggregate,
so that we first test whether we need to resolve as a record aggregate
(if the aggregate is not homogeneous), followed by testing whether the
type has an Aggregate aspect and calling Resolve_Container_Aggregate.
As a bonus, we also remove the subsequent complex condition and redundant
code for handling null container aggregates.

gcc/ada/

	* sem_aggr.adb (Resolve_Aggregate): Move condition and call for
	Resolve_Record_Aggregate in front of code related to calling
	Resolve_Container_Aggregate (and add test that the aggregate is
	not homogeneous), and remove special-case testing and call to
	Resolve_Container_Aggregate for empty aggregates. Also, add error
	check for an attempt to use "[]" for an aggregate of a record type
	that does not specify an Aggregate aspect.
	(Resolve_Record_Aggregate): Remove error check for record
	aggregates with "[]" (now done by Resolve_Aggregate).