RFR: 8315841: RISC-V: Check for hardware TSO support

[Ludovic Henry]

With the Ztso extension [1], some hardware will support TSO on RISC-V. That allows us to reduce the generation of memory fences, given the stronger memory model compared to RVWMO.

[1] https://github.com/riscv/riscv-isa-manual/blob/6dcbc6da9ada01f0f57da83cda6059bdec57619f/src/ztso-st-ext.adoc#L1

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Commit messages:
 - 8315841: RISC-V: Check for hardware TSO support

Changes: https://git.openjdk.org/jdk/pull/15613/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15613&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315841
  Stats: 14 lines in 4 files changed: 13 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15613.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15613/head:pull/15613

PR: https://git.openjdk.org/jdk/pull/15613