[jdk21u] RFR: 8316645: RISC-V: Remove dependency on libatomic by adding cmpxchg 1b

[Aleksey Shipilev]

Clean backport on the way to improve Atomic support in 21u.

Note @robehn ;)

Additional testing:
 - [x] MacOS AArch64 server fastdebug, `gtest:Atomic`

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Commit messages:
 - Backport 93f662f4fc766c09492c8d4ce7048605325d2100
 - Backport fb055e7e5300958b2a6a290aa6783e8ede929d9a

Changes: https://git.openjdk.org/jdk21u/pull/325/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=325&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316645
  Stats: 124 lines in 3 files changed: 118 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u/pull/325.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/325/head:pull/325

PR: https://git.openjdk.org/jdk21u/pull/325