RFR: 8257673: Build fails without shenandoahgc after JDK-8257563

[Jie Fu]

Hi all,

Please review this one-line change, which fixes the build failure without shenandoahgc.

Testing:
 - Build tests without shenandoahgc and PCH on Linux/x64

Thanks.
Best regards,
Jie

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Commit messages:
 - 8257673: Build fails without shenandoahgc after JDK-8257563

Changes: https://git.openjdk.java.net/jdk/pull/1594/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1594&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257673
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1594.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1594/head:pull/1594

PR: https://git.openjdk.java.net/jdk/pull/1594