[jdk17u] RFR: 8261579: AArch64: Support for weaker memory ordering in Atomic

[Aleksey Shipilev]

On Mon, 8 Nov 2021 10:19:31 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Clean backport to improve AArch64 performance in selected places.
> 
> Addtional testing:
>  - [x] Linux AArch64 fastdebug build
>  - [x] Linux AArch64 fastdebug `tier1`
>  - [x] Linux AArch64 fastdebug `tier2`
>  - [ ] Linux AArch64 release, jcstress `-m quick`

Paging @theRealAph -- do you think this is ready (stable) to go to 17u? This would unblock some Shenandoah backports.

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PR: https://git.openjdk.java.net/jdk17u/pull/239