it should be possible to run "ant precommit" with java9 [LUCENE-7725]

Eventually we'll want to be sure that `ant precommit` works even if you are using java9.

This is currently not possible because the ECJ (Eclipse JDT based) javadoc linter we use doesn't work on java9 – so we're blocked on that, and the build.xml explicitly fails fast. (The fail fast logic in build.xml can currently be bypassed via a `-Dis.jenkins.build=true` system prop)

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Migrated from [LUCENE-7725](https://issues.apache.org/jira/browse/LUCENE-7725) by Chris M. Hostetter (@hossman), 1 vote, updated Mar 02 2017
Linked issues:
- #8777
- #8778

Start with build.xml and the ECJ-based javadoc linter setup used by ant precommit; inspect the Java 9 fail-fast logic and the is.jenkins.build bypass described in the issue. Done means ant precommit completes successfully on Java 9 without relying on that bypass.

Written by the indexing model from the issue text.