RFR: 8254672: ZGC: ZParallelOopsDo/ZSerialWeakOopsDo should use atomic load/store [v2]

[Per Liden]

> ZParallelOopsDo/ZSerialWeakOopsDo should use atomic load/store. This patch builds on the JDK-8254671, which is
> currently out for review, so only the last commit is part of this PR.

Per Liden has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains
one commit:

  8254672: ZGC: ZParallelOopsDo/ZSerialWeakOopsDo should use atomic load/store

-------------

Changes: https://git.openjdk.java.net/jdk/pull/630/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=630&range=01
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/630.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/630/head:pull/630

PR: https://git.openjdk.java.net/jdk/pull/630