[riscv-port-jdk17u:riscv-port] RFR: 8308997: RISC-V: Sign extend when comparing 32-bit value with zero instead of testing the sign bit

[Gui Cao]

Hi,
Please help review this backport to riscv-port-jdk17u.
Backport of [JDK-8308997](https://bugs.openjdk.org/browse/JDK-8308997). 
Because there is no [JDK-8294100](https://bugs.openjdk.org/browse/JDK-8294100), [JDK-8301496](https://bugs.openjdk.org/browse/JDK-8301496) here in riscv-port-jdk17u, it will show not clean.

Testing(release on unmacthed):
- [x] Tier1 tests
- [ ] Tier2 tests
- [ ] Tier3 tests

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Commit messages:
 - Backport 8308997: RISC-V: Sign extend when comparing 32-bit value with zero instead of testing the sign bit

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/67/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=67&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308997
  Stats: 57 lines in 9 files changed: 0 ins; 14 del; 43 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/67.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/67/head:pull/67

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/67