[jdk21u] RFR: 8316645: RISC-V: Remove dependency on libatomic by adding cmpxchg 1b

[Robbin Ehn]

On Mon, 6 Nov 2023 14:08:29 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Clean backport on the way to improve Atomic support in 21u.
> 
> Note @robehn ;)
> 
> Additional testing:
>  - [x] MacOS AArch64 server fastdebug, `gtest:Atomic`

Thank you!

-------------

Marked as reviewed by rehn (Committer).

PR Review: https://git.openjdk.org/jdk21u/pull/325#pullrequestreview-1715302493