Sigh POSIX timezone naming. The timezone for Anywhere on Earth
(https://en.wikipedia.org/wiki/Anywhere_on_Earth) is:
UTC-12 (https://en.wikipedia.org/wiki/UTC%E2%88%9212:00)

So the tzdata zone is Etc/GMT+12, thanks to POSIX timezone names:
https://en.wikipedia.org/wiki/Tz_database#Area