* cp-tree.h (operator_name_info_t): Add arity.
* lex.c (init_operators): Initialize it.
* mangle.c (write_conversion_operator_name): New function.
(write_unqualified_name): Use it.
(write_template_args): Accept template arguments as a TREE_LIST.
(write_expression): Adjust handling of qualified names to match
specification.