[jdk21u-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: 3518.69s user 84.97s system 840% cpu 7:08.71 total
after: 2241.98s user 61.99s system 2617% cpu 1:28.03 total

#Release
before: 1367.16s user 134.95s system 371% cpu 6:44.67 total
after: 1206.90s user 114.48s system 2548% cpu 51.848 total

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Commit messages:
 - Backport f61499c73fe03e2e3680d7f58a84183364c5c5ac

Changes: https://git.openjdk.org/jdk21u-dev/pull/418/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=418&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/jdk21u-dev/pull/418.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/418/head:pull/418

PR: https://git.openjdk.org/jdk21u-dev/pull/418