RFR: CODETOOLS-7902857: jcstress: Support split compilation modes

[Aleksey Shipilev]

The groundwork that uses CompilerDirectives facility finally allows us to compile the actor methods with different compilers. This should catch inconsistencies in different compilers using incompatible memory barrier schemes.

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Commit messages:
 - Split compilation modes

Changes: https://git.openjdk.java.net/jcstress/pull/16/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=16&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902857
  Stats: 479 lines in 11 files changed: 380 ins; 27 del; 72 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/16.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/16/head:pull/16

PR: https://git.openjdk.java.net/jcstress/pull/16