test/ruby/test_set.rb: mmtk doesn't have GC.compact

Author: byroot

test/ruby/test_set.rb

@@ -874,7 +874,10 @@ def x
     end
 
     x
-    GC.compact
+    begin
+      GC.compact
+    rescue NotImplementedError
+    end
     end;
   end
 end