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).

As a solution we introduce a new method  `os::vm_shm_allocation_granularity()`, which on all platforms except AIX returns the same value as  `os::vm_allocation_granularity()`, but on AIX it returns (in the apropriate cases) 256MB.

This new getter is used at all needed places instead of  `os::vm_allocation_granularity()`.

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Commit messages:
 - JDK-8322943

Changes: https://git.openjdk.org/jdk/pull/17708/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17708&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322943
  Stats: 47 lines in 11 files changed: 28 ins; 9 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/17708.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17708/head:pull/17708

PR: https://git.openjdk.org/jdk/pull/17708