Fix riscv64 for no-std

[theoparis]

See issue #8768

[alexcrichton]

Thanks for this!

[stlankes]

The latest release (22.0) is 2 days old and doesn't include this PR. Is this what is intended?

[cfallin]

Is this what is intended?

Yes! Our release process is to branch the release branch on the 5th of each month, and let things be tested and bugs be discovered on main for at least two weeks (backporting fixes as needed) then release from that branch on the 20th. This ensures that every change and new feature has between two and six weeks of testing and fuzzing.

We didn't always do things this way but the procedure is from hard-earned experience where changes slipped in just before release have almost no testing and can cause problems. This PR should be included in the next release (23.0) on July 20.

You can see a bit more about the rationale in #3955.

[stlankes]

Sounds like a reasonable strategy!