RFR: 7903662: Javadoc generated by jextract breaks javac compilation

[Maurizio Cimadamore]

This is a backport of https://github.com/openjdk/jextract/pull/209 into the "master" branch.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jextract/pull/213/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=213&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903662
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/213.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/213/head:pull/213

PR: https://git.openjdk.org/jextract/pull/213