RFR: 8283238: make/scripts/compare.sh should show the diff when classlist does not match

[Calvin Cheung]

Please review this change for enabling verbose (-vv) when running the compare.sh script so that the diff between files will be available in the build stdout file. This is for troubleshooting the two bugs ([JDK-8283220](https://bugs.openjdk.org/browse/JDK-8283220), [JDK-8295951](https://bugs.openjdk.org/browse/JDK-8295951)) which happened intermittently.

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Commit messages:
 - 8283238: make/scripts/compare.sh should show the diff when classlist does not match

Changes: https://git.openjdk.org/jdk/pull/11192/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11192&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8283238
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11192.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11192/head:pull/11192

PR: https://git.openjdk.org/jdk/pull/11192