RFR: CODETOOLS-7903068: JMH: Enable compiler blackholes by default, if available [v2]

[Aleksey Shipilev]

> With the release of JDK 17, we can finally consider enabling [compiler blackholes](https://shipilev.net/jvm/anatomy-quarks/27-compiler-blackholes/) by default.

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Reconcile the meaning of "default" Blackhole mode

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Changes:
  - all: https://git.openjdk.java.net/jmh/pull/57/files
  - new: https://git.openjdk.java.net/jmh/pull/57/files/8ada9f99..47828f8a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmh&pr=57&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmh&pr=57&range=00-01

  Stats: 6 lines in 1 file changed: 1 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jmh/pull/57.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/57/head:pull/57

PR: https://git.openjdk.java.net/jmh/pull/57