RFR: 8271855: [TESTBUG] Wrong weakCompareAndSet assumption in UnsafeIntrinsicsTest

[Martin Doerr]

We need a fix for test failures due to wrong assumption. (See JBS issue for details.) I suggest to give weakCompareAndSet a 2nd chance.

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Commit messages:
 - Retry up to 4 times.
 - Fix comments.
 - 8271855: [testbug] Wrong weakCompareAndSet assumption in UnsafeIntrinsicsTest

Changes: https://git.openjdk.java.net/jdk/pull/4992/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4992&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271855
  Stats: 14 lines in 1 file changed: 6 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4992.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4992/head:pull/4992

PR: https://git.openjdk.java.net/jdk/pull/4992