[crac] RFR: Fix CPUFeatures crash on new->old CPU [v2]

[Jan Kratochvil]

> - reproducible on i7-1165G7 "qemu-kvm -cpu host" for a checkpoint and "qemu-kvm -cpu SandyBridge" for its restore

Jan Kratochvil has updated the pull request incrementally with four additional commits since the last revision:

 - Make _ignore_cpu_features a tri-state.
 - Fix up double call of VM_Version::crac_restore_finalize().
    - found by Randim Vansa
 - Move IgnoreCPUFeatures_local into the header.
    - suggested by Radim Vansa
 - Move CracSHM::_prefix to crac_posix.cpp
    - suggested by Radim Vansa

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

Changes:
  - all: https://git.openjdk.org/crac/pull/134/files
  - new: https://git.openjdk.org/crac/pull/134/files/d26f972a..f9470978

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=134&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=134&range=00-01

  Stats: 56 lines in 5 files changed: 24 ins; 15 del; 17 mod
  Patch: https://git.openjdk.org/crac/pull/134.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/134/head:pull/134

PR: https://git.openjdk.org/crac/pull/134