[11u] RFR (S) 8260704: ParallelGC: oldgen expansion needs release-store for _end

[Aleksey Shipilev]

Original bug:
   https://bugs.openjdk.java.net/browse/JDK-8260704
   https://git.openjdk.java.net/jdk16/commit/afd5eefd

While the patch is simple, 11u does not have Atomic methods we need -- those were moved from 
OrderAccess to Atomic in JDK 14 with JDK-8234562. So, 11u patch uses OrderAccess.

11u variant:
   https://cr.openjdk.java.net/~shade/8260704/webrev.11u.02/

Testing: tier{1,2} with Parallel

-- 
Thanks,
-Aleksey