RFR: 8343555: RISC-V: make UseZvfh diagnostic option

[Fei Yang]

On Mon, 4 Nov 2024 18:33:00 GMT, Hamlin Li <mli at openjdk.org> wrote:

> Hi,
> Can you help to review this simple patch?
> Previously this UseZvfh was changed from experimental to product because we have real hardware to verify the feature, but as pointed out by @RealFYang , this one should ber a diagnostic option, as we don't want to expose too many options to users.
> Thanks

Thanks. That make sense to me. Since we are having more and more RISC-V extensions, we should rely on linux hwprobe syscall for auto detection and enablement them in the long run. Seems that we should also similarly handle other ones like `UseRVC`, `UseRVV`, etc.

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21885#pullrequestreview-2414414743