RFR: 8307997: gtest:ZIndexDistributorTest fails on PPC64

[Stefan Karlsson]

ZindexDistributorTest was written with the assumption that `ZCacheLineSize == 64`, which isn't the case on PPC. I've updated the test to handle this case.

Tested by temporarily changing ZCacheLineSize to 128. I also added two more cases just to disambiguate the counts in one of the test.

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Commit messages:
 - 8307997: gtest:ZIndexDistributorTest fails on PPC64

Changes: https://git.openjdk.org/jdk/pull/13977/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13977&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307997
  Stats: 14 lines in 1 file changed: 9 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/13977.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13977/head:pull/13977

PR: https://git.openjdk.org/jdk/pull/13977