RFR: 8251944: Add Shenandoah test config to compiler/gcbarriers/UnsafeIntrinsicsTest.java [v2]

[Aleksey Shipilev]

> There used to be failures in Shenandoah CAS handling code like that were caught by this test. Those were fixed in JDK-8255401. This change turns the test into regression test for it.
> 
> Additional testing:
>  - [x] Affected test on `x86_64` fastdebug, release
>  - [x] Affected test on `x86_32` fastdebug
>  - [x] Affected test on `aarch64` fastdebug

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 four additional commits since the last revision:

 - Merge branch 'master' into JDK-8251944-shenandoah-test-unsafe
 - Mention 8255401 in @bug
 - Make test pass in release
 - 8251944: Add Shenandoah test config to compiler/gcbarriers/UnsafeIntrinsicsTest.java

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1693/files
  - new: https://git.openjdk.java.net/jdk/pull/1693/files/8ca12686..073e166c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1693&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1693&range=00-01

  Stats: 3353 lines in 229 files changed: 2017 ins; 565 del; 771 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1693.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1693/head:pull/1693

PR: https://git.openjdk.java.net/jdk/pull/1693