cpp/chrono/tai clock/from utc

Converts the  to a  representing the same point in time.

Return value
A std representing the same point in time as, computed as if by constructing a value of the return type from and adding. (378691210 is the number of seconds between the epochs of the two clocks: 1958-01-01 00:00:00 TAI and 1970-01-01 00:00:00 UTC.)