To cleanup the ant buildsystem (and to understand what is needed and what could be removed) I moved jars containing the ant-tasks to a subdirectory and load them with a single classloader definition.
I deleted the ant.jar because the build itself uses the installed ant version on the system.
Why I've did such step: I want to integrate a dependency management build with the ant-maven-tasks but its a bit tricky because the lib-folder is messy.
we figured out: the ant.jar is needed for jspc creation. It has been restored.