[tz] localtime_r multiple times slower for Europe/Moscow timezone

[Paul Eggert]

This is a known performance issue in glibc; see:

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

It'd be nice if someone found the time to fix it; perhaps that could be you?

The bug depends on how the TZif files are built. On my Fedora 37 
platform if you build with 'zic -b fat' Europe/Berlin is way faster than 
Europe/Moscow, but if you build with 'zic -b slim' it's the other way 
round. Obviously performance shouldn't be that much affected by whether 
TZif files are fat or slim.