RFR: JDK-8322943: runtime/CompressedOops/CompressedClassPointers.java fails on AIX

[Joachim Kern]

Even after recent fixes like
https://bugs.openjdk.org/browse/JDK-8305765
the test runtime/CompressedOops/CompressedClassPointers.java fails on AIX.

This error results from the fact, that on AIX the shmat() allocation granularity is 256MB instead of the standard Pagesize (4KB or 64KB).

Because my first proposal (PR 17708) of introducing a new method os::vm_shm_allocation_granularity() in the shared hotspot code was rejected I now encapsulate the difference in ifdef AIX brackets.

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Commit messages:
 - JDK-8322943

Changes: https://git.openjdk.org/jdk/pull/18105/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18105&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322943
  Stats: 96 lines in 4 files changed: 79 ins; 7 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/18105.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18105/head:pull/18105

PR: https://git.openjdk.org/jdk/pull/18105