[jdk16u] RFR: 8251944: Add Shenandoah test config to compiler/gcbarriers/UnsafeIntrinsicsTest.java

[Aleksey Shipilev]

This improves coverage for Shenandoah. This test fails without JDK-8255401 and passes with it.

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Commit messages:
 - Backport db6f39302b972a468452e2c2b7200039b2c23556

Changes: https://git.openjdk.java.net/jdk16u/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=50&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251944
  Stats: 24 lines in 1 file changed: 22 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/50/head:pull/50

PR: https://git.openjdk.java.net/jdk16u/pull/50