[Ada] Restore missing Aggregate aspect for Ada.Containers.Ordered_Sets.Set

[Marc Poulhiès via Gcc-patches]

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.
diff --git a/gcc/ada/libgnat/a-coorse.ads b/gcc/ada/libgnat/a-coorse.ads
--- a/gcc/ada/libgnat/a-coorse.ads
+++ b/gcc/ada/libgnat/a-coorse.ads
@@ -57,9 +57,9 @@ is
    type Set is tagged private
    with Constant_Indexing => Constant_Reference,
         Default_Iterator  => Iterate,
-        Iterator_Element  => Element_Type;
-        --  Aggregate         => (Empty       => Empty,
-        --                        Add_Unnamed => Include);
+        Iterator_Element  => Element_Type,
+        Aggregate         => (Empty       => Empty,
+                              Add_Unnamed => Include);
 
    pragma Preelaborable_Initialization (Set);