RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v15]

[Evgeny Astigeevich]

On Thu, 11 Nov 2021 11:35:17 GMT, Andrew Haley <aph at openjdk.org> wrote:

> I'm a bit concerned that it took so much effort to find a convincing benchmark, but I note that OnSpinWaitInst=isb doesn't seem to make anything worse, so OK.

Thank you  Andrew.
It took the time to study the current use cases of `Thread.onSpinWait` why they got performance improved or did not. As usual when you have written something simple you need to check it is correct. All of these took most of the time.

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PR: https://git.openjdk.java.net/jdk/pull/5562