Add client_state struct.

Collect per client specific global data items into struct client_state,
which is similar in purpose to remote.c::remote_state.

gdbserver/ChangeLog
	* server.h (struct client_state): New.
	* server.c (cont_thread, general_thread, multi_process)
	(report_fork_events, report_vfork_events, report_exec_events)
	(report_thread_events, swbreak_feature, hwbreak_feature)
	(vCont_supported, disable_randomization, pass_signals)
	(program_signals, program_signals_p, last_status, last_ptid, own_buf):
	Moved to client_state.
	* remote-utils.c (remote_debug, noack_mode)
	(transport_is_reliable): Moved to client_state.
	* tracepoint.c (current_traceframe): Moved to client_state.

	Update all callers.
	* server.c, remote-utils.c, tracepoint.c, fork-child.c,
	linux-low.c, remote-utils.h, target.c: Use client_state.