On KitKat, calling tzset with UTC+nn doesn't initialize all the
timezone state. If the previous timezone was something like
America/Chicago, then changing it to UTC+nn might have no effect.
Setting the timezone to an intermediate value like "UTC" avoids the
problem.
Works around https://github.com/android/ndk/issues/1604.
PiperOrigin-RevId: 413050236
Change-Id: I99b2d3330ae68f1d58cd2ca278d3eaae30bd1e83