CUnionEntity should inherit CStructEntity.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@8297 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/dl/lib/dl/struct.rb

@@ -160,7 +160,7 @@ module DL
     end
   end
 
-  class CUnionEntity < CStruct
+  class CUnionEntity < CStructEntity
     include PackInfo
 
     def CUnionEntity.malloc(types, func=nil)