Add "executing" property to threads.

	Add "executing" property to threads.

	* inferior.h (target_executing): Delete.
	* gdbthread.h (struct thread_info): Add executing_ field.
	(set_executing, is_executing): New.
	* thread.c (main_thread_executing): New.
	(init_thread_list): Clear it and also main_thread_running.
	(is_running): Return false if target has no execution.
	(any_running, is_executing, set_executing): New.

	* top.c: Include "gdbthread.h".
	(target_executing): Delete.
	(execute_command): Replace target_executing check by any_running.
	* event-top.c: Include "gdbthread.h".
	(display_gdb_prompt, command_handler): Replace target_executing by
	is_running.
	* inf-loop.c: Include "gdbthread.h".  Don't mark as not executing
	here.  Replace target_executing by is_running.
	* infrun.c (handle_inferior_event): Mark all threads as
	not-executing.
	* linux-nat.c (linux_nat_resume): Don't mark thread as executing
	here.
	* stack.c (get_selected_block): Return null if inferior is
	executing.
	* target.c (target_resume): Mark resumed ptid as executing.
	* breakpoint.c (until_break_command): Replace target_executing
	check by is_executing.
	* remote.c (remote_async_resume): Don't mark inferior as executing
	here.
	* mi/mi-interp.c (mi_cmd_interpreter_exec): Replace target_executing
	by any_running.

	* mi/mi-main.c (mi_cmd_exec_interrupt, mi_cmd_execute)
	(mi_execute_async_cli_command): Replace target_executing by
	is_running.

	* frame.c (get_current_frame): Error out if the current thread is
	executing.
	(has_stack_frames): New.
	(get_selected_frame, deprecated_safe_get_selected_frame): Check
	has_stack_frames.

	* Makefile.in (event-top.o, frame.o, inf-loop.o, top.o): Depend on
	$(gdbthread_h).