More Mac build fixes.

The libziparchive public headers that refer to `off64_t` also need the
Mac workaround.

In fastboot, there's a stray `lseek64` but since it's only for offset 0,
any kind of seek is fine.

Bug: N/A
Test: builds
Change-Id: I68b4f95202623ebf07ffe6c3e0e21437e7922c5b