How can I build the source code of IntelliJ-IDEA v9?

Hello, there!
Before asking this question, I have read this article following by this address:
http://www.jetbrains.org/pages/viewpage.action?pageId=983225 .
When I build the source code, the console report five errors those point to build.xml(line 17 & line 38).
Then I checked my JetGroovy plugin, the plugin is enabled.
The console information said {project_home}/build/gant.xml (line 18) gantfile does not exist. Which gant script file?
I paste the content of gant.xml:

<project name="Test gant invocation from Ant script" default="doGant">
  <dirname property="build.dir" file="${ant.file}"/>
  <property name="project.home" value="${build.dir}/.."/>
  <property name="gant.home" value="${project.home}/build/lib/gant"/>

  <path id="gant.classpath">
    <pathelement location="${project.home}/build/lib/gant_patches.jar"/>
    <fileset dir="${gant.home}/lib">
      <include name="*.jar"/>
    </fileset>
  </path>

  <taskdef name="gant" classname="org.codehaus.gant.ant.Gant">
    <classpath refid="gant.classpath"/>
  </taskdef>

  <target name="doGant">
    <gant file="${gant.script}"/>
  </target>
</project>