RFR: 8298225: [AIX] Disable PPC64LE continuations on AIX [v2]

[Tyler Steele]

> This small change adds an import to the generated ad_ppc.cpp file to allow it to find Contiuations::enabled, and sets VMContinuations to false on AIX.

Tyler Steele has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11550/files
  - new: https://git.openjdk.org/jdk/pull/11550/files/347a1091..347a1091

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11550&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11550&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11550.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11550/head:pull/11550

PR: https://git.openjdk.org/jdk/pull/11550