RFR: 8296805: ctw build is broken

[Roland Westrelin]

I noticed the build for the ctw tool based on the WhiteBox API is
broken. This fixes it AFAICT.

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/11090/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11090&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296805
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11090.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11090/head:pull/11090

PR: https://git.openjdk.org/jdk/pull/11090