You want to create tasks and types for an Ant build, or set global Ant properties.
Select Window Preferences Ant Runtime, and click the Tasks, Types, or Properties tabs.
If you click the Tasks and Types tabs, you can add new Ant tasks and types. Those tasks and types then will be available to build files without having to use Ant <taskdef> or <typedef> elements. Eclipse also enables you to set global Ant properties, across all projects, if you click the Properties tab in this dialog. To add a new global property, just click the Add button in the Properties tab, and enter a name and value for the new property.