Decode current time directly to timespec

Decode current time directly to timespec

* src/timefns.c (decode_time_components): If FASTER_TIMEFNS, when
returning the current time and the desired form is struct timespec
or time_t, return it directly rather than converting it to struct
ticks_hz and then to struct timespec.  This can avoid some mpz
calculations and/or bignums.

(cherry picked from commit e8b3c4cb58ce6e78b9bcfb9146f0ac6ece0d3055)