RFR: 8365543: [aix] Java_sun_nio_fs_UnixNativeDispatcher_init needs adjustment for AIX for some system call functions

[Matthias Baesken]

Java_sun_nio_fs_UnixNativeDispatcher_init currently misses to set the correct OS functions for my_openat_func and my_fstatat_func on AIX ; this should be adjusted.

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Commit messages:
 - JDK-8365543

Changes: https://git.openjdk.org/jdk/pull/26793/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26793&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365543
  Stats: 16 lines in 2 files changed: 7 ins; 8 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26793.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26793/head:pull/26793

PR: https://git.openjdk.org/jdk/pull/26793