The JDT Debug project is run the same way as the Debug Platform project.

To get started, follow the instructions specified in the "Contributing to the Debug Platform" document.

NOTE: The Debug Platform instructions for setting up a selfhosting workspace tell you how to check the Debug Platform projects out of CVS. To work with the JDT Debug projects, check out the following projects instead:
  org.eclipse.jdt.debug
  org.eclipse.jdt.debug.ui
  org.eclipse.jdt.debug.tests (optional)
  org.eclipse.jdt.debug.jdi.tests (optional)
  org.eclipse.jdt.launching (optional)
  org.eclipse.jdt.launching.j9 (optional)
  org.eclipse.jdt.launching.macosx (optional)