RFR: 7902762: JMH: Use "blackhole" compiler command

[Aleksey Shipilev]

On Thu, 19 Nov 2020 11:18:07 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> JMH can be enabled to use the "blackhole" compile command from [JDK-8252505](https://bugs.openjdk.java.net/browse/JDK-8252505).

> @shipilev
> I am very happy to see the black hole can be a compile option in JDK.
> As I did not see any documentation, I am wondering if it has any impact on the usage of Blackhole? Specifically, I mean `JMHSample_09_Blackholes.java `. If yes, could you also provide new examples about how to use it?

There should be no operational impact, and all current samples should continue to work.

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PR: https://git.openjdk.java.net/jmh/pull/8