Automatic download of junit.jar seems to be broken. If you don't already have a copy in tools/java, "ant all" fails like this:
The problem seems to be that junit_check refuses to continue if the junit property is set, but does not point to an existing file. This property is set when the setCompilerProperties target, which runs before junit_check, loads tools/ant/properties/extrapath.properties, as extrapath.properties contains the following line:
Since the install_junit target depends on the check_junit target, this prevents the build script from downloading junit.jar automatically.
Workaround: run "ant install_junit" before "ant all"