RFR: 8316440: LambdasInTwoArchives.java failed to find WhiteBox.class

[Calvin Cheung]

Please review this simple test fix for adding build of `jdk.test.whitebox.WhiteBox`.

Passed tier1 testing.

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Commit messages:
 - 8316440: LambdasInTwoArchives.java failed to find WhiteBox.class

Changes: https://git.openjdk.org/jdk/pull/15805/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15805&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316440
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15805.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15805/head:pull/15805

PR: https://git.openjdk.org/jdk/pull/15805