RFR: 8312180: (bf) MappedMemoryUtils passes incorrect arguments to msync (aix) [v2]

[Tyler Steele]

> This change is as an alternate solution to my original proposal for [JDK-8312180](https://bugs.openjdk.org/browse/JDK-8312180).
> 
> Suggested by @tstuefe.
> 
> This change matches the return value of Bits.pageSize with the system page size (which is not currently true on AIX).
> 
> These tests are upstream of my target test (TestByteBuffer) and results are encouraging. Tier1 testing in ongoing for this change.

Tyler Steele has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains two new commits since the last revision:

 - Removes include unistd & replaces it with util/globalDefs.hpp
 - Replace os::vm_page_size call with sysconf(_SC_PAGESIZE) on AIX in javaClasses.cpp

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14963/files
  - new: https://git.openjdk.org/jdk/pull/14963/files/15d0a7f8..3d940994

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14963&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14963&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14963.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14963/head:pull/14963

PR: https://git.openjdk.org/jdk/pull/14963