RFR: 7902762: JMH: Use "blackhole" compiler command [v6]

[Aleksey Shipilev]

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

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge branch 'master' into CODETOOLS-7902762
 - Unlock compiler blackholes as needed
 - Copyrights in new file
 - Print experimental support option
 - Touchups
 - Update to new JDK prototype: don't use DONT_INLINE
 - 7902762: JMH: Use "blackhole" compiler command

-------------

Changes:
  - all: https://git.openjdk.java.net/jmh/pull/8/files
  - new: https://git.openjdk.java.net/jmh/pull/8/files/db0b3b7c..48a985d3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmh&pr=8&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jmh&pr=8&range=04-05

  Stats: 753 lines in 36 files changed: 501 ins; 178 del; 74 mod
  Patch: https://git.openjdk.java.net/jmh/pull/8.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/8/head:pull/8

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