[jdk24u] RFR: 8343607: C2: Shenandoah crashes during barrier expansion in Continuation::enter

[Roland Westrelin]

Clean backport of this shenandoah c2 fix. We hit this bug when running the tck for 24.

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Commit messages:
 - Backport 45c914c3ad8fbc406af9ba9dec97f11c28c91299

Changes: https://git.openjdk.org/jdk24u/pull/155/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk24u&pr=155&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343607
  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk24u/pull/155.diff
  Fetch: git fetch https://git.openjdk.org/jdk24u.git pull/155/head:pull/155

PR: https://git.openjdk.org/jdk24u/pull/155