[jdk21u-dev] RFR: 8319777: Zero: Support 8-byte cmpxchg

[Aleksey Shipilev]

Clean backport to improve Zero support.

Additional testing:
 - [x] Linux x86_32 Zero, `jcstress` run
 - [x] Large matrix of Zero builds

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Commit messages:
 - Backport 06d957fd7c1ff59f314315969a545a8f4a5137be
 - Backport 6b96bb640aa91d96877b8ceea5fed359607c1e45

Changes: https://git.openjdk.org/jdk21u-dev/pull/232/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=232&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319777
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/232.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/232/head:pull/232

PR: https://git.openjdk.org/jdk21u-dev/pull/232