[crac] RFR: Implement: -XX:+UseZGC is currently unsupported for -XX:CRaCCheckpointTo

[Jan Kratochvil]

Implement: -XX:+UseZGC is currently unsupported for -XX:CRaCCheckpointTo

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Commit messages:
 - Add the exception message.
 - Implement: -XX:+UseZGC is currently unsupported for -XX:CRaCCheckpointTo

Changes: https://git.openjdk.org/crac/pull/90/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=90&range=00
  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/90.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/90/head:pull/90

PR: https://git.openjdk.org/crac/pull/90