RFR: 8350266: [PPC64] Interpreter: intrinsify Thread.currentThread()

[David Linus Briemann]

Implementation of intrinsic Thread.currentThread() for PPC64.

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Commit messages:
 - implement generate_currentThread for PPC

Changes: https://git.openjdk.org/jdk/pull/23677/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23677&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350266
  Stats: 14 lines in 1 file changed: 13 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23677.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23677/head:pull/23677

PR: https://git.openjdk.org/jdk/pull/23677