[crac] RFR: 8373784: [CRaC] VM Option to require perfect CPU fit [v2]

[Radim Vansa]

> Right now CRaC will refuse to restore from the image if it is not compatible with current CPU as it assumes extra features. This check can be only relaxed with -XX:+UnlockExperimentalVMOptions -XX:+IgnoreCPUFeatures.
> 
> In scenarios with -XX:CRaCIgnoreRestoreIfUnavailable it might be favorable to skip the restore and proceed with running the application from scratch with all CPU features if the image has these restricted. Therefore I propose to create a new option -XX:CheckCPUFeatures with these values:
> * compatible - this is the current behaviour (default)
> * exact - require CPU features from the image to match perfectly
> * skip - the same behaviour as `-XX:+IgnoreCPUFeatures`.
> 
> The current `-XX:+IgnoreCPUFeatures` option will be deprecated.

Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:

  Minor fixups

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

Changes:
  - all: https://git.openjdk.org/crac/pull/285/files
  - new: https://git.openjdk.org/crac/pull/285/files/c9ed0a90..75db21c9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=285&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=285&range=00-01

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/crac/pull/285.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/285/head:pull/285

PR: https://git.openjdk.org/crac/pull/285