[jdk21u-dev] RFR: 8316961: Fallback implementations for 64-bit Atomic::{add,xchg} on 32-bit platforms

[Aleksey Shipilev]

Clean backport to complete Atomics support and make future backports safe.

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

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Commit messages:
 - Backport ba7d08b8199172058bd369d880d2d6a9f9649319

Changes: https://git.openjdk.org/jdk21u-dev/pull/233/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=233&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316961
  Stats: 108 lines in 5 files changed: 97 ins; 8 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/233.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/233/head:pull/233

PR: https://git.openjdk.org/jdk21u-dev/pull/233