RFR: Merge jdk8u:master

[Andrew John Hughes]

Merge jdk8u352-b03

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Commit messages:
 - Merge jdk8u352-b03
 - 8071507: (ref) Clear phantom reference as soft and weak references do

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=shenandoah-jdk8u&pr=25&range=00.0
 - jdk8u:master: https://webrevs.openjdk.org/?repo=shenandoah-jdk8u&pr=25&range=00.1

Changes: https://git.openjdk.org/shenandoah-jdk8u/pull/25/files
  Stats: 173 lines in 10 files changed: 105 ins; 48 del; 20 mod
  Patch: https://git.openjdk.org/shenandoah-jdk8u/pull/25.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk8u.git pull/25/head:pull/25

PR: https://git.openjdk.org/shenandoah-jdk8u/pull/25