I should have remembered that we can't use INT64_MODIFIER with sscanf():
configure chooses that to work with snprintf(), but it might be for our
src/port/snprintf.c implementation and so not compatible with the
platform's sscanf().  This appears to be the explanation for buildfarm
member frogmouth's continuing unhappiness with the tzcode update.

Fortunately, in all of the places where zic is attempting to read into
an int64 variable, it's reading a year which certainly will fit just fine
into an int.  So make it read into an int with %d, and then cast or copy
as necessary.