RFR: 8314139: TEST_BUG: runtime/os/THPsInThreadStackPreventionTest.java could fail on machine with large number of cores

[Man Cao]

Hi all, @tstuefe 

Could anyone review this fix for a test failure that could happen on machines with many cores? This fix caps `-XX:ActiveProcessorCount` to 64, which limits the number of internal threads the JVM creates.

An alternative is to bump up the `acceptableRSSLimitMB` such as increasing `basicRSSOverheadMB`. However, this approach could be fragile for machines with even more number of cores (e.g. 256 or more).

-Man

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Commit messages:
 - 8314139: TEST_BUG: runtime/os/THPsInThreadStackPreventionTest.java could fail on machine with large number of cores

Changes: https://git.openjdk.org/jdk/pull/15241/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15241&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314139
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15241.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15241/head:pull/15241

PR: https://git.openjdk.org/jdk/pull/15241