RFR: 8302368: [ZGC] Client build fails after JDK-8300255

[Jie Fu]

Hi all,

Please review this small change to fix the client vm build failure.

"__" redefined [-Werror] occurred if build without C2.

Thanks.
Best regards,
Jie

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Commit messages:
 - 8302368: [ZGC] Client build fails after JDK-8300255

Changes: https://git.openjdk.org/jdk/pull/12547/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302368
  Stats: 11 lines in 3 files changed: 3 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12547.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12547/head:pull/12547

PR: https://git.openjdk.org/jdk/pull/12547