further support for struct/union tags

Author: Daniel Kroening

src/util/type.cpp

@@ -99,7 +99,9 @@ bool is_constant_or_has_constant_components(
   // we have to use the namespace to resolve to its definition:
   // struct t { const int a; };
   // struct t t1;
-  if(type.id() == ID_symbol_type)
+  if(type.id() == ID_symbol_type ||
+     type.id() == ID_struct_tag ||
+     type.id() == ID_union_tag)
   {
     const auto &resolved_type = ns.follow(type);
     return has_constant_components(resolved_type);