sync with userland: let z_off_t fall back to long long instead of long

sync with userland: let z_off_t fall back to long long instead of long

In the boot blocks, this would result in various 64-bit instruction being
used, which might result in undesirable bloat in legacy boot loaders, so
add a workaround for the _STANDALONE case to still fall back to long
instead of long long.

with/ok deraadt, ok millert