Modify NEON check for ARM64 on OS X (#48982)
Summary:
Use CMAKE_SYSTEM_PROCESSOR rather than run sysctl
Fixes https://github.com/pytorch/pytorch/issues/48874
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48982
Reviewed By: walterddr
Differential Revision: D25385883
Pulled By: malfet
fbshipit-source-id: 47b6dc5be8d75f6d4a66a11c564abdfe31ac90b4
