The man page for tzfile(5) makes it clear that timezone files are
written in a portable format (big-endian always). So it is feasible to
run zic on the build system in a cross-compile.
Surely the simplest fix is to provide a configure option allows the use
of the host systems own /zic /command? Something like --with-system-zic.
Then cross compiles from any Unix-like system with a suitable zic will
work fine.
Richard