RFR: 8321282: RISC-V: SpinPause() not implemented [v2]

[Robbin Ehn]

> Hi, please consider.
> 
> Tested tier1 and targeted via gtest WaitBarrier which uses SpinPause(). (with UseZihintpause default true)

Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:

  Removed memory clobber

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17820/files
  - new: https://git.openjdk.org/jdk/pull/17820/files/5043aaab..3af1c6d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17820&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17820&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17820.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17820/head:pull/17820

PR: https://git.openjdk.org/jdk/pull/17820