[jdk21u-dev] RFR: 8343724: [PPC64] Disallow OptoScheduling

[Martin Doerr]

Clean backport of [JDK-8343724](https://bugs.openjdk.org/browse/JDK-8343724).

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Commit messages:
 - Backport f621f26cd113090a0305598cfc50f0eac9a263c6

Changes: https://git.openjdk.org/jdk21u-dev/pull/1153/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1153&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343724
  Stats: 39 lines in 2 files changed: 22 ins; 16 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1153.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1153/head:pull/1153

PR: https://git.openjdk.org/jdk21u-dev/pull/1153