[jdk17u] RFR: 8270098: ZGC: ZBarrierSetC2::clone_at_expansion fails with "Guard against surprises" assert

[Tobias Hartmann]

Backport of [JDK-8270098](https://bugs.openjdk.java.net/browse/JDK-8270098). Applies cleanly.

-------------

Commit messages:
 - 8270098: ZGC: ZBarrierSetC2::clone_at_expansion fails with "Guard against surprises" assert

Changes: https://git.openjdk.java.net/jdk17u/pull/16/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=16&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270098
  Stats: 106 lines in 2 files changed: 83 ins; 11 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/16.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/16/head:pull/16

PR: https://git.openjdk.java.net/jdk17u/pull/16