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

[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.

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jmh/pull/57/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmh&pr=57&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903068
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 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