code: def is_union(declaration):
      
      if not is_class(declaration):
          return False
      decl = class_traits.get_declaration(declaration)
      return decl.class_type == class_declaration.CLASS_TYPES.UNION
docs: Returns True if declaration represents a C++ union
  
      Args:
          declaration (declaration_t): the declaration to be checked.
  
      Returns:
          bool: True if declaration represents a C++ union