[PATCH RESEND] x86_64: make atomic64_t work like atomic_t

Regardless of the greater controversy about the semantics of atomic_t, I think we can all agree that atomic_t and atomic64_t should have the same semantics. This is presently not the case on x86_64, where the volatile keyword was removed from the declaration of atomic_t, but it was not removed

[PATCH RESEND] x86_64: make atomic64_t work like atomic_t

Regardless of the greater controversy about the semantics of atomic_t, I think we can all agree that atomic_t and atomic64_t should have the same semantics. This is presently not the case on x86_64, where the volatile keyword was removed from the declaration of atomic_t, but it was not removed