[jdk17u-dev] RFR: 8355632: WhiteBox.waitForReferenceProcessing() fails assert for return type

[Goetz Lindenmaier]

I backport this for parity with 17.0.19-oracle.

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Commit messages:
 - Backport bf52eb035865353fdf5c6c242f9676a51dcc9e22

Changes: https://git.openjdk.org/jdk17u-dev/pull/4234/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=4234&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355632
  Stats: 31 lines in 2 files changed: 30 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/4234.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/4234/head:pull/4234

PR: https://git.openjdk.org/jdk17u-dev/pull/4234