Ada RM A.18.9 includes a specification of the Aggregate aspect for the type
Ada.Containers.Ordered_Sets. That aspect specification was deliberately
commented out in a-coorse.ads at one time, but that workaround is no longer
needed.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* libgnat/a-coorse.ads: Restore Aggregate aspect specification for
	type Set.