Remote all-stop-on-top-of-non-stop

This is the first pass at implementing support for all-stop mode
running against the remote target using the non-stop variant of the
protocol.

The trickiest part here is the initial connection setup/synching.  We
need to fetch all inferiors' target descriptions etc. before stopping
threads, because stop_all_threads needs to read the threads' registers
(to record each thread's stop_pc).  But OTOH, the initial inferior
setup (target_post_attach, post_create_inferior, etc.), only works
correctly if the inferior is stopped...  So I've split that initial
setup part from attach_command_post_wait to a separate function, and
added a "still needs setup" flag to the inferior structure.  This is
similar to gdbserver/linux-low.c's handling of discovering the
process's target description).  Then if on connection all threads of
the remote inferior are running, when we go about stopping them, as
soon as they stop we call setup_inferior, from within
stop_all_threads.

Also, in all-stop, we need to process all the initial stop replies to
learn about all the pending signal the threads may already be stopped
for, and pick the one to report as current.  This is exposed by
gdb.threads/reconnect-signal.exp.

gdb/
2015-11-30  Pedro Alves  <palves@redhat.com>

	* gdbthread.h (switch_to_thread_no_regs): Declare.
	* infcmd.c (setup_inferior): New function, factored out from ...
	(attach_command_post_wait): ... this.  Rename to ...
	(attach_post_wait): ... this.  Replace parameter async_exec with
	attach_post_wait_mode parameter.  Adjust.
	(enum attach_post_wait_mode): New enum.
	(struct attach_command_continuation_args): Replace 'async_exec'
	field with 'mode' field.
	(attach_command_continuation): Adjust.
	(attach_command): Add comment.  Mark the inferior as needing
	setup.  Adjust to use enum attach_post_wait_mode.
	(notice_new_inferior): Use switch_to_thread_no_regs.  Adjust to
	use enum attach_post_wait_mode.
	* inferior.h (setup_inferior): Declare.
	(struct inferior) <needs_setup>: New field.
	* infrun.c (set_last_target_status): Make extern.
	(stop_all_threads): Make extern.  Setup inferior, if necessary.
	* infrun.h (set_last_target_status, stop_all_threads): Declare.
	* remote-notif.c (remote_async_get_pending_events_handler)
	(handle_notification): Replace non_stop checks with
	target_is_non_stop_p() checks.
	* remote.c (remote_notice_new_inferior): Remove non_stop check.
	(remote_update_thread_list): Replace non_stop check with
	target_is_non_stop_p() check.
	(print_one_stopped_thread): New function.
	(process_initial_stop_replies): New 'from_tty' parameter.
	"Notice" all new live inferiors after storing initial stops as
	pending status in each corresponding thread.  If all-stop, stop
	all threads, try picking a signalled thread as current, and print
	the status of that one thread.  Record the last target status.
	(remote_start_remote): Replace non_stop checks with
	target_is_non_stop_p() checks.  Don't query for the remote current
	thread of use qOffsets here.  Pass from_tty to
	process_initial_stop_replies.
	(extended_remote_attach): Replace non_stop checks with
	target_is_non_stop_p() checks.
	(extended_remote_post_attach): Send qOffsets here.
	(remote_vcont_resume, remote_resume, remote_stop)
	(remote_interrupt, remote_parse_stop_reply, remote_wait): Replace
	non_stop checks with target_is_non_stop_p() checks.
	(remote_async): If target is non-stop, mark/clear the pending
	events token.
	* thread.c (switch_to_thread_no_regs): New function.

gdb/gdbthread.h

@@ -411,9 +411,14 @@ extern struct thread_info *iterate_over_threads (thread_callback_func, void *);
 
 extern int thread_count (void);
 
-/* Switch from one thread to another.  */
+/* Switch from one thread to another.  Also sets the STOP_PC
+   global.  */
 extern void switch_to_thread (ptid_t ptid);
 
+/* Switch from one thread to another.  Does not read registers and
+   sets STOP_PC to -1.  */
+extern void switch_to_thread_no_regs (struct thread_info *thread);
+
 /* Marks or clears thread(s) PTID as resumed.  If PTID is
    MINUS_ONE_PTID, applies to all threads.  If ptid_is_pid(PTID) is
    true, applies to all threads of the process pointed at by PTID.  */