Support running FreeBSD buildworld on Arm-based macOS hosts

Arm-based Macs are like FreeBSD and provide a full 64-bit stat from the
start, so have no stat64 variants. Thus, define stat64 and fstat64 as
aliases for the normal versions.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>
Closes #11771