TZ magic in ESP/M5Unified

[wsanders]

Mt RTC is set to UTC. Somehow, this magically works:

    setenv("TZ","PST8PDT",1);
    tzset();
    auto tm = localtime(&t);
    M5.Display.printf("ESP32 %04d/%02d/%02d (%s)  %02d:%02d:%02d\r\n",
          tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday,
          wd[tm->tm_wday],
          tm->tm_hour, tm->tm_min, tm->tm_sec);

Just posting here in case someone is mystified by the Rtc.ino example, since it doesn't set the TZ "environment variable" the calls to localtime and gmtime will return the same.