RFR: 8309475: Test java/foreign/TestByteBuffer.java fails: a problem with msync (aix)

[Tyler Steele]

This change adds additional support to MappedByteBuffer::force which delegates to msync on AIX. Specifically, it checks whether and error with errno set to EINVAL is the cause of a msync call to an address mmapped with the MAP_PRIVATE flag set. If this flag is set, then the msync call EINVAL is expected, and can be ignored as per the Java documentation of the force method.

> In particular, the method has no effect for buffers mapped in read-only or private mapping modes. [1]

Separated into separate file as per recommendation by @AlanBateman.

[1] https://download.java.net/java/early_access/jdk21/docs/api/java.base/java/nio/MappedByteBuffer.html#force()

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Depends on: https://git.openjdk.org/jdk/pull/14963

Commit messages:
 - Maintain linux-specific definition for minicore_vec_t
 - Separate AIX MappedMemoryUtils to new file. Add force0 implementation
 - Replace vm_page_size call with sysconf(_SC_PAGESIZE) in javaClasses.cpp

Changes: https://git.openjdk.org/jdk/pull/14964/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14964&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309475
  Stats: 233 lines in 2 files changed: 210 ins; 23 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14964.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14964/head:pull/14964

PR: https://git.openjdk.org/jdk/pull/14964