[jdk21u-dev] RFR: 8342014: RISC-V: ZStoreBarrierStubC2 clobbers rflags

[Gui Cao]

Hi, The same issue also exists in the jdk21u. I would like to backport this to jdk21u-dev. becasue jdk21u-dev not have [JDK-8334060](https://bugs.openjdk.org/browse/JDK-8334060), so this backport is not clean. This is a risc-v specific change, risk is low.

# Testing
- [ ]  Run tier1-3 tests on SOPHON SG2042 (release)

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Commit messages:
 - Backport 8342014: RISC-V: ZStoreBarrierStubC2 clobbers rflags

Changes: https://git.openjdk.org/jdk21u-dev/pull/1059/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1059&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342014
  Stats: 30 lines in 2 files changed: 0 ins; 0 del; 30 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1059.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1059/head:pull/1059

PR: https://git.openjdk.org/jdk21u-dev/pull/1059