This bug affects hosts where time_t is unsigned, which AFAICT does
not include anything we currently support. (It _does_ include
OpenVMS, about a month of BSD4.2's history[1], and a lot of the 1970s.)
There are probably more bugs when time_t is unsigned. This one was
[1] http://mail-index.netbsd.org/tech-userlevel/1998/06/04/0000.html
Inspired by #8042.
As far as I know, OpenVMS is the only place you're likely to hit an
unsigned time_t these days, and Tor's VMS support
is... lacking. Still worth letting people know about it, though.
