[jdk21u-dev] RFR: 8314842: zgc/genzgc tests ignore vm flags

[Goetz Lindenmaier]

I backport this to keep the tests up-to-date. Many similar changes have been backported. Let's do this, too, to complete the job. This will simplify later backports.

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Commit messages:
 - Backport ae75ca05e450da577e712eb7ed9dd9203616b80b

Changes: https://git.openjdk.org/jdk21u-dev/pull/1623/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1623&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314842
  Stats: 6 lines in 6 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1623.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1623/head:pull/1623

PR: https://git.openjdk.org/jdk21u-dev/pull/1623