1  struct tree_decl
       2  {
       3    unsigned in_system_header_flag:1;
       4  };
       5  union tree_node
       6  {
       7    struct tree_decl decl;
       8  };
       9  typedef union tree_node *tree;
      10  static int
      11  redeclaration_error_message (olddecl)
      12       tree olddecl;
      13  {
      14    if (({olddecl;})->decl.in_system_header_flag)
      15      ;
      16  }