* inferiors.c (struct thread_info): Add gdb_id.

	(add_thread): Add gdb_id argument.
	(thread_id_to_gdb_id, thread_to_gdb_id, gdb_id_to_thread_id): New.
	* linux-low.c (linux_create_inferior, linux_attach_lwp): Update
	calls to add_thread.
	* remote-utils.c (prepare_resume_reply: Use thread_to_gdb_id.
	* server.c (handle_query): Use thread_to_gdb_id.
	(handle_v_cont, main): Use gdb_id_to_thread_id.
	* server.h (add_thread): Update prototype.
	(thread_id_to_gdb_id, thread_to_gdb_id, gdb_id_to_thread_id): New
	prototypes.