RFR: 8307495: Specialize atomic bitset functions for aix-ppc

[David Briemann]

Also refactor so that linux and aix use the same code for ppc.

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Commit messages:
 - minor fixes
 - fix copyright headers
 - 8307495: Specialize atomic bitset functions for aix-ppc

Changes: https://git.openjdk.org/jdk/pull/27650/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27650&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307495
  Stats: 1536 lines in 6 files changed: 665 ins; 854 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/27650.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27650/head:pull/27650

PR: https://git.openjdk.org/jdk/pull/27650