pending interrupts.
* interrupts.c (interrupts_process): Keep track of the last number
of masked insn cycles.
(interrupts_initialize): Clear last number of masked insn cycles.
(interrupts_info): Report them.
(interrupts_update_pending): Compute clear and set masks of
interrupts and clear the interrupt bits before setting them
(due to SCI interrupt sharing).
* interrupts.h (struct interrupts): New members last_mask_cycles
and xirq_last_mask_cycles.
* dv-m68hc11tim.c (cycle_to_string): New function to translate
the cpu cycle into some formatted time string.
(m68hc11tim_print_timer): Use it.
* dv-m68hc11sio.c (m68hc11sio_info): Use cycle_to_string.
* dv-m68hc11spi.c (m68hc11spi_info): Likewise.
* interrupts.c (interrupts_info): Likewise.
* m68hc11_sim.c (cpu_info): Likewise.
