ada: Lift technical limitation in expansion of record aggregates

ada: Lift technical limitation in expansion of record aggregates

The mechanim deferring the expansion of record aggregates nested in other
aggregates with intermediate conditional expressions is disabled in the
case where they contain self-references, because of a technical limitation
in the replacements done by Build_Record_Aggr_Code.  This change lifts it.

gcc/ada/ChangeLog:

	* exp_aggr.adb (Traverse_Proc_For_Aggregate): New generic procedure.
	(Replace_Discriminants): Instantiate it instead of Traverse_Proc.
	(Replace_Self_Reference): Likewise.
	(Convert_To_Assignments): Remove limitation for nested aggregates
	that contain self-references.