time.c: introduce do_clock_gettime, do_clock_settime, and do_clock_nanosleep

time.c: introduce do_clock_gettime, do_clock_settime, and do_clock_nanosleep

These are going to be used to implement parsers of clock_gettime64,
clock_settime64, and clock_nanosleep_time64 syscalls.

* time.c (do_clock_settime, do_clock_gettime, do_clock_nanosleep): New
functions.
((SYS_FUNC(clock_settime)): Turn into a thin wrapper around
do_clock_settime.
((SYS_FUNC(clock_gettime)): Turn into a thin wrapper around
do_clock_gettime.
((SYS_FUNC(clock_nanosleep)): Turn into a thin wrapper around
do_clock_nanosleep.