[riscv-port-jdk17u:riscv-port] RFR: 8305728: RISC-V: Use bexti instruction to do single-bit testing

[Fei Yang]

On Thu, 1 Jun 2023 09:30:05 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi, please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8305728](https://bugs.openjdk.org/browse/JDK-8305728). The original patch cannot be directly applied because jdk17u has no [JDK-8299089](https://bugs.openjdk.org/browse/JDK-8299089) and [JDK-8301995](https://bugs.openjdk.org/browse/JDK-8301995).
> 
> Testing:
> - tier1-3 tests on QEMU-System w/ and w/o UseZbs (release build)
> - tier1-3 tests on unmatched board w/o UseZbs (release build)

Looks good. Thanks.

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Marked as reviewed by fyang (Lead).

PR Review: https://git.openjdk.org/riscv-port-jdk17u/pull/65#pullrequestreview-1456565300