[jdk18u] RFR: 8279668: x86: AVX2 versions of vpxor should be asserted [v2]

[Aleksey Shipilev]

> Clean backport to prevent SIGILLs on incompatible hardware.
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug with `-XX:UseAVX=1`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8279668-vpxor-asserts
 - Backport 2bbeae3f056243a224b0bda021f16cdcbee3b3d6

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

Changes:
  - all: https://git.openjdk.java.net/jdk18u/pull/39/files
  - new: https://git.openjdk.java.net/jdk18u/pull/39/files/16edabd7..bd56b8ae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=39&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=39&range=00-01

  Stats: 217 lines in 6 files changed: 192 ins; 5 del; 20 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/39.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/39/head:pull/39

PR: https://git.openjdk.java.net/jdk18u/pull/39