RFR: 8315856: RISC-V: Use Zacas extension for cmpxchg [v3]

[Ludovic Henry]

> 8315856: RISC-V: Use Zacas extension for cmpxchg

Ludovic Henry has updated the pull request incrementally with one additional commit since the last revision:

  fix merge conflict mistake

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16910/files
  - new: https://git.openjdk.org/jdk/pull/16910/files/b9d86703..16b42595

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16910&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16910&range=01-02

  Stats: 6 lines in 1 file changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16910.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16910/head:pull/16910

PR: https://git.openjdk.org/jdk/pull/16910