Move type stack handling to a new class

Move type stack handling to a new class

This introduces a new "type_stack" class, and moves all the parser
type stack handling to this class.  Parsers that wish to use this
facility must now instantiate this class somehow.  I chose this
approach because a minority of the existing parsers require this.

gdb/ChangeLog
2019-04-04  Tom Tromey  <tom@tromey.com>

	* type-stack.h: New file.
	* type-stack.c: New file.
	* parser-defs.h (enum type_pieces, union type_stack_elt): Move to
	type-stack.h.
	(insert_into_type_stack, insert_type, push_type, push_type_int)
	(insert_type_address_space, pop_type, pop_type_int)
	(pop_typelist, pop_type_stack, append_type_stack)
	(push_type_stack, get_type_stack, push_typelist)
	(follow_type_instance_flags, follow_types): Don't declare.
	* parse.c (type_stack): Remove global.
	(parse_exp_in_context): Update.
	(insert_into_type_stack, insert_type, push_type, push_type_int)
	(insert_type_address_space, pop_type, pop_type_int)
	(pop_typelist, pop_type_stack, append_type_stack)
	(push_type_stack, get_type_stack, push_typelist)
	(follow_type_instance_flags, follow_types): Remove (moved to
	type-stack.c).
	* f-exp.y (type_stack): New global.
	Update rules.
	(push_kind_type, f_parse): Update.
	* d-exp.y (type_stack): New global.
	Update rules.
	(d_parse): Update.
	* c-exp.y (struct c_parse_state) <type_stack>: New member.
	Update rules.
	* Makefile.in (COMMON_SFILES): Add type-stack.c.
	(HFILES_NO_SRCDIR): Add type-stack.h.