RFR: 8350716: [s390] intrinsify Thread.currentThread()

[Amit Kumar]

s390x port for [JDK-8278793](https://bugs.openjdk.org/browse/JDK-8278793)

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Commit messages:
 - currentThread Intrinsic

Changes: https://git.openjdk.org/jdk/pull/23791/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23791&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350716
  Stats: 13 lines in 1 file changed: 12 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23791.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23791/head:pull/23791

PR: https://git.openjdk.org/jdk/pull/23791