Fix the open solaris atomic functions on arm64. Without this we may use the
wrong value in the comparison, leading to incorrectly setting the new
value.

This has been observed in the ZFS code. Without this we can lose track of
the reference count in a zrlock object.

We should move to use the generic atomic functions, however as this has
been observed I would prefer to have this working, then move to the generic
functions.

PR: 204037
Sponsored by: ABT Systems Ltd