RFR: 8255606: Enable concurrent stack processing on x86_32 platforms

[Zhengyu Gu]

8255606: Enable concurrent stack processing on x86_32 platforms

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Commit messages:
 - Merge branch 'master' into JDK-8255606-conc-stack-x86_32
 - 8255606: Enable concurrent stack processing on x86_32 platforms

Changes: https://git.openjdk.java.net/jdk/pull/945/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=945&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255606
  Stats: 63 lines in 7 files changed: 34 ins; 14 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/945.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/945/head:pull/945

PR: https://git.openjdk.java.net/jdk/pull/945