RFR: 8307295: Add warning to not create new ACC flags

[Coleen Phillimore]

Please comment on or review this new comment.  Thanks.

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Commit messages:
 - 8307295: Add warning to not create new ACC flags

Changes: https://git.openjdk.org/jdk/pull/13757/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13757&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307295
  Stats: 6 lines in 1 file changed: 2 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13757.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13757/head:pull/13757

PR: https://git.openjdk.org/jdk/pull/13757