RFR: 8345177: RISC-V: Add gtests for cmpxchg [v2]

[Robbin Ehn]

> Hi, please consider.
> 
> This adds tests to some of the base cases.
> Focusing on the cases when we pass in same register in some of the argument. (variant 0,1,2,3)
> 
> Note: Google Test filter = *RiscV.cmpxchg*
> [==========] Running 4 tests from 1 test suite.
> [----------] Global test environment set-up.
> [----------] 4 tests from RiscV
> [ RUN      ] RiscV.cmpxchg_int64_plain_lr_sc_vm
> [       OK ] RiscV.cmpxchg_int64_plain_lr_sc_vm (2 ms)
> [ RUN      ] RiscV.cmpxchg_int64_plain_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_int64_plain_maybe_zacas_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_int32_plain_lr_sc_vm
> [       OK ] RiscV.cmpxchg_int32_plain_lr_sc_vm (0 ms)
> [ RUN      ] RiscV.cmpxchg_int32_plain_maybe_zacas_vm
> [       OK ] RiscV.cmpxchg_int32_plain_maybe_zacas_vm (0 ms)
> [----------] 4 tests from RiscV (20806 ms total)
> 
> [----------] Global test environment tear-down
> [==========] 4 tests from 1 test suite ran. (20809 ms total)
> [  PASSED  ] 4 tests.
> 
> 
> Executed with `-XX:+UnlockExperimentalVMOptions -XX:+UseZacas`
> 
> Thanks, Robbin

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

  Remove CMF barrier

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22437/files
  - new: https://git.openjdk.org/jdk/pull/22437/files/48dc0423..b5a18748

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22437&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22437&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22437.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22437/head:pull/22437

PR: https://git.openjdk.org/jdk/pull/22437