[tz] Bad 32 bit data in 2018f

[Paul Eggert]

Thanks for the heads-up. I confirmed that tzcode 2015f (and earlier) 
when compiled for 32-bit time_t misreads the 32-bit binary (TZif) files 
generated by tzdb 2018f. I'll try to come up with a fix soon, most 
likely by having zic insert a dummy transition or two in the 32-bit 
data. As a temporary workaround you can continue to use 2018e zic to 
compile from .zi to TZif.

Recommended practice nowadays is for 32-bit client code to ignore 32-bit 
binary data entirely, and to just use the 64-bit data, discarding any 
timestamps outside the 32-bit range. This is why tests with 2018f didn't 
catch the problem. However, we should support 32-bit clients that don't 
follow the recommended practice.