Generate aggregate Javadoc without duplicate execution of phase compile.

• The standard goals aggregate and test-aggregate invoke separate lifecycles compile and test-compile.
• In a CI environment you now might execute something like mvn clean deploy site site-deploy.
• During site build the standard reports will trigger compile or test-compile again, depending on your build this may take some time, because stuff like enforcer or generating stubs from a WSDL will be invoked again, which may lead to longer build times.
• As of version 3.0.1 two new reports are defined, aggregate-no-fork and test-aggregate-no-fork which will not trigger above phases a second time.
• Configure this in your reporting section as follows:

  <project>
   ...
   <reporting>
   <excludeDefaults>true</excludeDefaults>
   <plugins>
   <plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-javadoc-plugin</artifactId>
   <version>3.12.0</version>
   <reportSets>
   <reportSet>
   <reports>
   <report>aggregate-no-fork</report>
   <report>test-aggregate-no-fork</report>
   </reports>
   </reportSet>
   </reportSets>
   </plugin>
   </plugins>
   </reporting>
   ...
  </project>