RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v8]

[Nick Gasson]

On Tue, 28 Sep 2021 21:34:39 GMT, Evgeny Astigeevich <github.com+42899633+eastig at openjdk.org> wrote:

>> I have a fix which makes the test working with or without hsdis. I am testing it.
>
> Done.

The [IR test framework](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/compiler/lib/ir_framework/README.md) can parse the C2 opto assembly output, and also control compilation level and flags through method annotations. I'm not sure if we could use that to check the C1 output though. Maybe @chhagedorn has some ideas?

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