[8, 11] RFC: [backport] 8235636: gc/shenandoah/compiler/TestUnsafeOffheapSwap.java fails after JDK-8226411

[Aleksey Shipilev]

This had slipped under our backporting radar, because it had no relevant affected versions:
  https://bugs.openjdk.java.net/browse/JDK-8235636?

It looks like triggered by JDK-8226411, but the actual issue is generic. Applying that patch over 8u
seems to resolve some of the Cassandra crashes I have been chasing recently.

OK to backport to 8u/11u? 11u applies cleanly. 8u applies with reshuffling

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey