RFR: Allow forcing the use of compiler hints using a system property

[Gilles Duboscq]

Using `-Djmh.compilerhints.mode=true` will force the use of compiler hints. `-Djmh.compilerhints.mode=false` will prevent the use of compiler hints. When the system property is not set, the current beahviour based on vm name and version will be used by default.

This is especially useful when working with uncommon / rare JVMs or when adding compiler hints support to a new JVM.

I considered auto-detecting support for compiler hints but that didn't fit very well in the current code and required much more intrusive changes.

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

Commit messages:
 - Allow forcing the use of compiler hints using a system property

Changes: https://git.openjdk.org/jmh/pull/96/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=96&range=00
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jmh/pull/96.diff
  Fetch: git fetch https://git.openjdk.org/jmh pull/96/head:pull/96

PR: https://git.openjdk.org/jmh/pull/96