Attached.

  I tried to make it as simple and musl-coding-style-compliant as possible.
  One line adds support for TZif3 (it costs nothing once we have TZif2 and
we can ignore the extensions).
  The other changes are ifdef-guarded and can be ignored with -DNO_LEAPSECONDS,
for hardcore POSIX fans. ;) But posix/ rules don't have leap seconds anyway,
only right/ ones do: if you don't like #ifdef forests, feel free to remove the
guards.

  By the way, what's the musl policy on internal sanity checks ? In __tz.c,
musl doesn't check anything after the magic numbers, so if the zoneinfo file
is bad later on, musl can crash, or worse, silently return inconsistent or
wrong results. I understand that it's impossible to escalate an error to the
user when the entry point returns a void, but wouldn't it be safer, in this
case as well as in similar cases, to abort the program ? I tend to think that
even raising a SIGSEGV manually would be better than silent undefined
behaviour.

  I can also confirm that strftime() fails to null-terminate its output in some
circumstances, most likely when the format string ends with a regular character
instead of a conversion specifier. I'll submit a patch as soon as I have time to
investigate more, unless you can fix it before I get to it.

-- 
  Laurent