[crac] RFR: Support -XX:CPUFeatures=ignore during -XX:CRaCRestoreFrom

[Jan Kratochvil]

Support -XX:CPUFeatures=ignore during -XX:CRaCRestoreFrom

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Commit messages:
 - Document -XX:CPUFeatures=ignore, reject !ignore during -XX:CRaCRestoreFrom
 - Support -XX:CPUFeatures=ignore during -XX:CRaCRestoreFrom

Changes: https://git.openjdk.org/crac/pull/100/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=100&range=00
  Stats: 37 lines in 4 files changed: 32 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/crac/pull/100.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/100/head:pull/100

PR: https://git.openjdk.org/crac/pull/100