RFR: 8376350: Convert ReferenceProcessorPhaseTimes to use Atomic<T>

[Thomas Schatzl]

Hi all,

  please review this change to convert `ReferenceProcessorPhaseTimes` to use `Atomic<T>`.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - 8376350

Changes: https://git.openjdk.org/jdk/pull/29423/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29423&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376350
  Stats: 9 lines in 2 files changed: 2 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/29423.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29423/head:pull/29423

PR: https://git.openjdk.org/jdk/pull/29423