RFR: 8186670: Implement _onSpinWait() intrinsic for AArch64 [v4]

[Evgeny Astigeevich]

On Thu, 23 Sep 2021 14:09:12 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> As Andrew suggested to have separated options for the name and the count, this won't be an issue.
>
> It was more of a question than a suggestion. I'm not sure, and I'd like you to have a look at existing options to see if there's a precedent.

I like the suggestion to have them separated. It makes code simpler. A separate `OnSpinWaitInstCount` uses standard ways to define it as an integer with a range. I don't need to write code for this. Problems with the combined approach start when a number of instructions to use needs to be more than 9.

I have found no precedent of combined options.

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