tor/changes/bug40383

  o Minor bugfixes (timekeeping):
    - Calculate the time of day correctly on systems where the time_t
      type includes leap seconds. (This is not the case on most
      operating systems, but on those where it occurs, our tor_timegm
      function did not correctly invert the system's gmtime function,
      which could result in assertion failures when calculating
      voting schedules.)  Fixes bug 40383; bugfix on 0.2.0.3-alpha.
Use native timegm when available. Continue having a tor_gmtime_impl() unit test so that we can detect any problems in our replacement function; add a new test function to make sure that gmtime<->timegm are a round-trip on now-ish times. This is a fix for bug #40383, wherein we ran into trouble because tor_timegm() does not believe that time_t should include a count of leap seconds, but FreeBSD's gmtime believes that it should. This disagreement meant that for a certain amount of time each day, instead of calculating the most recent midnight, our voting-schedule functions would calculate the second-most-recent midnight, and lead to an assertion failure. I am calling this a bugfix on 0.2.0.3-alpha when we first started calculating our voting schedule in this way. 2021-06-01 22:18:23 +02:00			`o Minor bugfixes (timekeeping):`
			`- Calculate the time of day correctly on systems where the time_t`
			`type includes leap seconds. (This is not the case on most`
			`operating systems, but on those where it occurs, our tor_timegm`
			`function did not correctly invert the system's gmtime function,`
			`which could result in assertion failures when calculating`
			`voting schedules.) Fixes bug 40383; bugfix on 0.2.0.3-alpha.`