RFR: 8345177: RISC-V: Add gtests for cmpxchg

[Robbin Ehn]

Hi, please consider.

This adds 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

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

Commit messages:
 - fixed ws
 - gtest cmpxchg 4/8

Changes: https://git.openjdk.org/jdk/pull/22437/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22437&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345177
  Stats: 156 lines in 1 file changed: 156 ins; 0 del; 0 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