Falcon compiler javadoc build shows errors due to missing classpath dependencies

The Ant javadoc target in compiler/build.xml generates a number of errors, e.g.:

[javadoc] Constructing Javadoc information...
[javadoc] /home/raju/src/svn/falcon-svn/compiler/src/org/apache/flex/compiler/ant/COMPCTask.java:26: package org.apache.tools.ant does not exist
[javadoc] import org.apache.tools.ant.BuildException;
[javadoc] ^
[javadoc] /home/raju/src/svn/falcon-svn/compiler/src/org/apache/flex/compiler/ant/COMPCTask.java:27: package org.apache.tools.ant does not exist
[javadoc] import org.apache.tools.ant.DynamicConfigurator;
[javadoc] ^
[javadoc] /home/raju/src/svn/falcon-svn/compiler/src/org/apache/flex/compiler/ant/FlexTask.java:31: package org.apache.tools.ant does not exist
[javadoc] import org.apache.tools.ant.BuildException;
(continues)

Apache Ant ant.jar is missing in the classpath, when I add ant.jar to the classpath for the javadoc target, no error message is shown.

<target name="javadoc" depends="as3.parser,metadata.parser,as3.codegen.emitter,as3.codegen.UnknownTreeHandler,css.codegen.emitter,css.grammar" description="Build javadoc">
<javadoc destdir="${javadoc}" useexternalfile="yes" overview="${src}/overview.html" failonerror="true">
<classpath>
<pathelement location="/usr/share/ant/lib/ant.jar"/>
<path refid="classpath" />
</classpath>