RFR: JDK-8322943: runtime/CompressedOops/CompressedClassPointers.java fails on AIX [v4]

[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.

Joachim Kern has updated the pull request incrementally with one additional commit since the last revision:

  reduce the amount of changed lines

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18105/files
  - new: https://git.openjdk.org/jdk/pull/18105/files/179b2474..33e2b056

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18105&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18105&range=02-03

  Stats: 69 lines in 1 file changed: 11 ins; 51 del; 7 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