RFR: 8317545: AIX PPC64: Implementation of Foreign Function & Memory API

[Martin Doerr]

The AIX linker has a few minor diffs to the linux ABIv1 linker. In addition, double values have only 4 Byte alignment.

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Commit messages:
 - Change double alignment to 4 in tests.
 - 8317545: AIX PPC64: Implementation of Foreign Function & Memory API

Changes: https://git.openjdk.org/jdk/pull/16179/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16179&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317545
  Stats: 325 lines in 15 files changed: 234 ins; 78 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/16179.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16179/head:pull/16179

PR: https://git.openjdk.org/jdk/pull/16179