[crac] RFR: Keep _features the same after CRaC restore

[Jan Kratochvil]

Extending `_features` may change ABI or existing JIT-compiled code. Unfortunately we cannot use more advanced CPU features after restore, we need to stick to the same features of CPU used to make the checkpoint file.

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

Commit messages:
 - Keep _features the same after CRaC restore

Changes: https://git.openjdk.org/crac/pull/103/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=103&range=00
  Stats: 22 lines in 1 file changed: 16 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/crac/pull/103.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/103/head:pull/103

PR: https://git.openjdk.org/crac/pull/103