strace.c: introduce struct tcb_wait_data

strace.c: introduce struct tcb_wait_data

Introduce a new structure to pass information between next_event(),
restart_delayed_tcb(), and dispatch_event().

This is going to be used by a subsequent change of next_event().

* strace.c (struct tcb_wait_data): New type.
(next_event): Remove parameters, return a pointer
to const struct tcb_wait_data.  Return NULL instead of TE_BREAK.
(dispatch_event): Replace all parameters with a pointer
to const struct tcb_wait_data, obtain the trace event, siginfo,
and status from its fields.
(restart_delayed_tcb): Add local struct tcb_wait_data variable
with te field set to TE_RESTART, pass it to dispatch_event().
(main): Remove status and si variables, update next_event()
and dispatch_event() invocations.

Co-Authored-by: Eugene Syromyatnikov <evgsyr@gmail.com>