Shenandoah and 11.0.5 backports

[Roman Kennke]

>> Or we could just wait until the fixes arrived via the usual channels.
>> How long would that take? Could we accept this?
> 
> Not sure. I mean, we can go ahead and try, but I believe at least JDK-8224580 is invalidating the
> invariant that LRB slowpath expects. I remember we were chasing the bad bug there. So if that bug
> happens again in sh/jdk11 after backports land, then what do we do?

Ah right, this was not performance-only. Nevermind then, we need this to
arrive before we go.

Roman