gdbserver: Use std::list for all_processes

Remove the usage of inferior_list for the all_processes list in
gdbserver, replace it with an std::list. The entry field in process_info
is removed, and replaced by a simple pid field.

The pid_of macro, used for both processes and threads, is replaced with
separate functions.  For completeness, I changed ptid_of and lwpid_of to
functions as well.

gdb/gdbserver/ChangeLog:

	* gdbthread.h (ptid_of, pid_of, lwpid_of): New functions.
	* inferiors.h: Include <list>.
	(struct process_info) <entry>: Remove field.
	<pid>: New field.
	(pid_of): Change macro to function.
	(ptid_of, lwpid_of): Remove macro.
	(all_processes): Change type to std::list<process_info *>.
	(ALL_PROCESSES): Remove macro.
	(for_each_process, find_process): New function.
	* inferiors.c (all_processes): Change type to
	std::list<process_info *>.
	(find_thread_process): Adjust.
	(add_process): Likewise.
	(remove_process): Likewise.
	(find_process_pid): Likewise.
	(get_first_process): Likewise.
	(started_inferior_callback): Remove.
	(have_started_inferiors_p): Adjust.
	(attached_inferior_callback): Remove.
	(have_attached_inferiors_p): Adjust.
	* linux-low.c (check_zombie_leaders): Likewise.
	* linux-x86-low.c (x86_arch_setup_process_callback): Remove.
	(x86_linux_update_xmltarget): Adjust.
	* server.c (handle_query): Likewise.
	(gdb_reattached_process): Remove.
	(handle_status): Adjust.
	(kill_inferior_callback): Likewise.
	(detach_or_kill_inferior): Remove.
	(print_started_pid): Likewise.
	(print_attached_pid): Likewise.
	(detach_or_kill_for_exit): Update.
	(process_serial_event): Likewise.
	* linux-arm-low.c (arm_new_fork): Likewise.