RFR: Merge openjdk/jdk21u:master

[William Kemper]

Merges tag jdk-21.0.8+6

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Commit messages:
 - 8357105: C2: compilation fails with "assert(false) failed: empty program detected during loop optimization"

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

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/198/files
  Stats: 66 lines in 2 files changed: 64 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/198.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/198/head:pull/198

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/198