[jdk8u-dev] RFR: 8211804: Constant AO_UNUSED_MBZ uses left shift of negative value

[Zdenek Zambersky]

Backport fixes left shift on negative value which is undefined behavior. This is required to build on newer clang (macos). See also [backport of JDK-8157758](https://github.com/openjdk/jdk8u-dev/pull/682).

File has different path on JDK 8, but changes applied cleanly.

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Commit messages:
 - Backport 44f94ee8bc6c934be1f4435227a81e6072361110

Changes: https://git.openjdk.org/jdk8u-dev/pull/722/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=722&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8211804
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/722.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/722/head:pull/722

PR: https://git.openjdk.org/jdk8u-dev/pull/722