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

[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.

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Depends on: https://git.openjdk.org/jdk/pull/11546

Commit messages:
 - Add continuation.hpp to adlc/main.cpp
 - Set VMContinuations to false on AIX

Changes: https://git.openjdk.org/jdk/pull/11550/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11550&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298225
  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 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