RFR (XS) 8225441: Cleanup ShenandoahHeap::atomic_compare_exchange_oop

[Aleksey Shipilev]

On 6/6/19 7:57 PM, Roman Kennke wrote:
> We could also just use RawAccess<>::oop_atomic_cmpxchg() instead. That
> does the same thing afaics. However, doing our owns is better
> backportable (to 8). What do you think?

Let's do this one for backports, and then the follow-up to use RawAccess, where available?

-Aleksey