RFR: 8304446: javap --system flag doesn't override system APIs

[Adam Sotona]

Javap ignores --system option when searching for JDK classes.
This patch prepends search over JDK system modules.

Please review.

Thanks,
Adam

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Commit messages:
 - 8304446: javap --system flag doesn't override system APIs

Changes: https://git.openjdk.org/jdk/pull/16476/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16476&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304446
  Stats: 12 lines in 1 file changed: 12 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16476.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16476/head:pull/16476

PR: https://git.openjdk.org/jdk/pull/16476