RFR: 8290: Handle resources warnings

[Marcus Hirt]

Seems to be an acceptable solution across tools.

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Commit messages:
 - 8290: Fixing resources warnings

Changes: https://git.openjdk.org/jmc/pull/606/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=606&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8290
  Stats: 5 lines in 4 files changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jmc/pull/606.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/606/head:pull/606

PR: https://git.openjdk.org/jmc/pull/606