[jdk21u] RFR: Merge jdk21:master

[Rob McKenna]

Merge jdk21

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Commit messages:
 - Merge
 - 8313316: Disable runtime/ErrorHandling/MachCodeFramesInErrorFile.java on ppc64le
 - 8300937: Update nroff pages in JDK 21 before RC
 - 8313260: JDK21: ProblemList java/lang/ScopedValue/StressStackOverflow.java on linux-x86
 - 8313241: Temporarily disable "malformed control flow" assert to reduce noise
 - 8313250: Exclude java/foreign/TestByteBuffer.java on AIX
 - 8312293: SIGSEGV in jfr.internal.event.EventWriter.putUncheckedByte after JDK-8312086
 - 8313208: ProblemList java/util/concurrent/tck/JSR166TestCase.java on select platforms
 - 8313193: ProblemList java/util/concurrent/SynchronousQueue/Fairness.java on X64

The merge commit only contains trivial merges, so no merge-specific webrevs have been generated.

Changes: https://git.openjdk.org/jdk21u/pull/30/files
  Stats: 176 lines in 33 files changed: 45 ins; 62 del; 69 mod
  Patch: https://git.openjdk.org/jdk21u/pull/30.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/30/head:pull/30

PR: https://git.openjdk.org/jdk21u/pull/30