RFR: RISC-V vthread support for JVM intrinsic monitors [v2]

[Fei Yang]

> This ported vthread support for JVM intrinsic monitors to linux-riscv64 platform.
> 
> Testing on linux-riscv64:
> - [x] make test TEST="hotspot_loom jdk_loom" (release & fastdebug)
> - [x] make test TEST=tier1/2/3 (release)
> - [x] make test TEST=hotspot:tier4 (release)

Fei Yang has updated the pull request incrementally with one additional commit since the last revision:

  Comment

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Changes:
  - all: https://git.openjdk.org/loom/pull/212/files
  - new: https://git.openjdk.org/loom/pull/212/files/663cad33..649a8b5a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=loom&pr=212&range=01
 - incr: https://webrevs.openjdk.org/?repo=loom&pr=212&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/loom/pull/212.diff
  Fetch: git fetch https://git.openjdk.org/loom.git pull/212/head:pull/212

PR: https://git.openjdk.org/loom/pull/212