RFR: 8316186: RISC-V: Remove PlatformCmpxchg<4>

Wed Sep 13 12:31:56 UTC 2023

Hi, please consider.

I don't know the history behind the Cmpxhg<4>, but it is not needed anymore.
Using compiler as in 8 byte case is just fine.

Passes hotspot-tier (qemu, vf2 still running), some manual extra testing via gtest, looked at compiler: output, e.g. https://godbolt.org/z/a31Gdqn8q

If you know the history please share, and if you have a reason why we should keep it please speak up!

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Commit messages:
 - Removed

Changes: https://git.openjdk.org/jdk/pull/15715/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15715&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316186
  Stats: 32 lines in 1 file changed: 0 ins; 32 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15715.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15715/head:pull/15715

PR: https://git.openjdk.org/jdk/pull/15715