RFR: 8328139: Prefer 'override' to 'virtual' in subclasses of 'GCInitLogger'

[Guoxiong Li]

Hi all,

This patch adds keyword `override` and removes `virtual` in the subclasses of `GCInitLogger`. 

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

-------------

Commit messages:
 - Prefer override to virtual.

Changes: https://git.openjdk.org/jdk/pull/18291/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18291&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328139
  Stats: 8 lines in 3 files changed: 1 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/18291.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18291/head:pull/18291

PR: https://git.openjdk.org/jdk/pull/18291