Some properties set in other places:
        <property name="launcher" location="${eclipse.home}/plugins/org.eclipse.equinox.launcher_1.1.0.v20100118.jar" />
        <property name="buildFile" location="${eclipse.home}/plugins/org.eclipse.pde.build_3.6.0.v20100123-1019/scripts/build.xml" />
        <property name="builder" location="${workspace}/projectName-build" />
        <property name="buildDirectory" location="${workspace}/output" />

Actual build:
        <target name="build" depends="setup,verifyBuild,removeBuildDir">
                <java jar="${launcher}" fork="yes" failonerror="true" dir="${builder}">
                        <jvmarg line="-Dbuilder=${builder} -DbuildDirectory=${buildDirectory} -DbaseLocation=${workspace} -Dworkspace=${workspace}" />
                        <arg line="-application org.eclipse.ant.core.antRunner -buildfile ${buildFile}" />
                </java>
        </target>