RFR: 8345179: RISC-V: Add gtests for weak cmpxchg [v3]

[Robbin Ehn]

> Hi, please consider.
> 
> This adds tests of aligned weak narrow cmpxchg.
> 
> [ RUN      ] RiscV.cmpxchg_weak_int16_lr_sc_vm
> [       OK ] RiscV.cmpxchg_weak_int16_lr_sc_vm (2 ms)
> [ RUN      ] RiscV.cmpxchg_weak_int8_lr_sc_vm
> [       OK ] RiscV.cmpxchg_weak_int8_lr_sc_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_weak_int16_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_weak_int16_maybe_zacas_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_weak_int8_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_weak_int8_maybe_zacas_vm (0 ms)
> [----------] 4 tests from RiscV (20997 ms total)
> 
> Executed with -XX:+UnlockExperimentalVMOptions -XX:+UseZacas
> 
> Thanks, Robbin

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

  Added weak 4/8 byte cmpxchg

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22476/files
  - new: https://git.openjdk.org/jdk/pull/22476/files/66cdf740..bb43ec8f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22476&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22476&range=01-02

  Stats: 68 lines in 1 file changed: 58 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/22476.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22476/head:pull/22476

PR: https://git.openjdk.org/jdk/pull/22476