* linux-nat.c (linux_nat_terminal_inferior)

	* linux-nat.c (linux_nat_terminal_inferior)
	(linux_nat_terminal_ours): Don't check sync_execution.
	* remote.c (remote_terminal_inferior, remote_terminal_ours):
	Don't check sync_execution.  Update comments.
	* target.c (target_terminal_inferior): New.
	* target.h (target_terminal_inferior): Delete macro, and declare
	as function.
	* event-top.c (async_disable_stdin): Make idempotent.  Don't give
	the target the terminal here.
	* inflow.c (terminal_ours_1): Don't return early without setting
	`terminal_is_ours'.