[jdk11u-dev] RFR: 8316608: Enable parallelism in vmTestbase/gc/vector tests

[Soumadipta Roy]

Backporting the fix for https://bugs.openjdk.org/browse/JDK-8316608 merged as part of openjdk/jdk#16028.
https://github.com/openjdk/jdk/commit/f61499c73fe03e2e3680d7f58a84183364c5c5ac.patch could be applied cleanly.

Run details on AL2_x86_64:

Fastdebug
before: 4741.91s user 91.12s system 588% cpu 13:41.56 total
after: 3451.17s user 43.90s system 3196% cpu 1:49.33 total

Release 11
before: 2905.04s user 93.12s system 394% cpu 12:39.98 total
after: 2745.40s user 57.49s system 3319% cpu 1:24.43 total

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Commit messages:
 - Backport f61499c73fe03e2e3680d7f58a84183364c5c5ac

Changes: https://git.openjdk.org/jdk11u-dev/pull/2630/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2630&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316608
  Stats: 299 lines in 13 files changed: 0 ins; 299 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2630.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2630/head:pull/2630

PR: https://git.openjdk.org/jdk11u-dev/pull/2630