ada: Small cleanups and fixes in expansion of aggregates

ada: Small cleanups and fixes in expansion of aggregates

This streamlines the handling of qualified expressions in the expansion of
aggregates and plugs a couple of loopholes that may cause memory leaks.

gcc/ada/

	* exp_aggr.adb (Build_Array_Aggr_Code): Move the declaration of Typ
	to the beginning.
	(Initialize_Array_Component): Test the unqualified version of the
	expression for the nested array case.
	(Initialize_Ctrl_Array_Component): Do not duplicate the expression
	here.  Do the pattern matching of the unqualified version of it.
	(Gen_Assign): Call Unqualify to compute Expr_Q and use Expr_Q in
	subsequent pattern matching.
	(Initialize_Ctrl_Record_Component): Do the pattern matching of the
	unqualified version of the aggregate.
	(Build_Record_Aggr_Code): Call Unqualify.
	(Convert_Aggr_In_Assignment): Likewise.
	(Convert_Aggr_In_Object_Decl): Likewise.
	(Component_OK_For_Backend): Likewise.
	(Is_Delayed_Aggregate): Likewise.