[lworld] RFR: 8341844: [lworld] Test crashing in genzgc in ZBarrier::mark_from_old_slow_path(zaddress)+0x4c

[David Simms]

Generational zgc requires a store barrier in addition to the load barrier.
load barrier followed by bulk copy isn't enough

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Commit messages:
 - 8341844: [lworld] Test crashing in genzgc in ZBarrier::mark_from_old_slow_path(zaddress)+0x4c

Changes: https://git.openjdk.org/valhalla/pull/1321/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1321&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341844
  Stats: 45 lines in 2 files changed: 33 ins; 5 del; 7 mod
  Patch: https://git.openjdk.org/valhalla/pull/1321.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1321/head:pull/1321

PR: https://git.openjdk.org/valhalla/pull/1321