newlib: Add adjtime - makes a gradual adjustment the system clock

newlib: Add adjtime - makes a gradual adjustment the system clock

This function speeds up or slows down the system clock in order to make a gradual adjustment. This ensures
 that the calendar time reported by the system clock is always monotonically increasing, which might not happen
 if you simply set the clock.

The delta argument specifies a relative adjustment to be made to the clock time. If negative, the system clock is
 slowed down for a while until it has lost this much elapsed time. If positive, the system clock is speeded up for a
 while.

If the olddelta argument is not a null pointer, the adjtime function returns information about any previous time
 adjustment that has not yet completed.

The return value is 0 on success and -1 on failure.

To stop the adjustement, call the function settimeofday(current_time).