Bug#893547: ant: please do not emit --ignore-source-errors on Java 9

[Ole Streicher]

Package: ant
Version: 1.9.9-6
Severity: serious

Dear maintainer,

to fix #884187, ant added the option "--ignore-source-errors" to
javadoc. This option is however not available on Java 9, which leads to
FTBFS on some packages: starjava-topcat, starjava-tools. I will merge
the relevant bug reports.

Best regards

Ole