RFR: 8254292: Update JMH devkit to 1.26

Fri Oct 9 13:12:09 UTC 2020

On Fri, 9 Oct 2020 12:30:35 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> It is currently at 1.21, and thus misses a bunch of fixes and improvements.
> 
> Testing:
>   - [x] Creating the JMH devkit
>   - [x] Using a new devkit with `make test TEST=micro:RecordDeserialization`

Marked as reviewed by erikj (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/575