cctools: Two fixes for x86-64 (Linux) host

1. stat.h from x86-64 Linux headers declares __unused as an array
   but we have it as a define. May be better to avoid __unused
   altogether as it's quite messy.

2. Change definition of __uint64_t and __int64_t in Darwin headers
   (inclde/i386/_types.h) to match that from Linux x86-64.