Use std::vector in type stacks

Use std::vector in type stacks

This removes the use of VEC from parse.c and, at the same time,
removes some related cleanups from c-exp.y.

gdb/ChangeLog
2019-01-06  Tom Tromey  <tom@tromey.com>

	* parser-defs.h (type_ptr): Remove typedef.  Don't declare VEC.
	(union type_stack_elt) <typelist_val>: Now a pointer to
	std::vector.
	(type_stack_cleanup): Don't declare.
	(push_typelist): Update.
	* parse.c (pop_typelist): Return a std::vector.
	(push_typelist): Take a std::vector.
	(follow_types): Update.  Do not free args.
	(type_stack_cleanup): Remove.
	* c-exp.y (struct c_parse_state): New.
	(cpstate): New global.
	(type_aggregate_p, exp, ptr_operator, parameter_typelist)
	(nonempty_typelist): Update.
	(func_mod): Create a new vector.
	(c_parse): Create a c_parse_state.
	(check_parameter_typelist): Do not delete params.
	(function_method): Update.  Do not delete type_list.