This is in preparation for the mach thread id rework, which requires 64 bit there (and incidentally also stops truncating the FreeBSD one).
There wasn't any direct usage of `__int64` in the sever protocol before, so I added a new typedef and a new `dump_int64()` function (not sure if needed per se though).
-- v4: ntdll: Remove unneeded FreeBSD codepath in get_unix_tid(). server, ntdll: Use 64 bit for unix thread id.