Ant: Classe introuvable: javac1. 8

J'essaie de construire un projet en utilisant Ant dans eclipse. J'ai cliqué droit sur construire.xml > exécuter en tant que > Ant Build. Cependant, je reçois l'erreur suivante:

BUILD FAILED
C:UsersDavideclipsetest-projectbuild.xml:26: Class not found: javac1.8

Et aussi un avertissement:

compile:
[javac] C:UsersDavideclipsetest-projectbuild.xml:26: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds

Comme je l'ai lu dans d'autres messages que cela pourrait être dû à une version ant trop ancienne ou ne pas avoir correctement défini les variables d'environnement, voici toutes les informations:

C:>java -version
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)

C:>ant -version
Apache Ant(TM) version 1.9.3 compiled on December 23 2013

C:>echo %JAVA_HOME%
C:Program FilesJavajdk1.8.0_05

C:>echo %JRE_HOME%
C:Program FilesJavajre8

Modifier: Voici l'ensemble de la construction.xml, ligne 26 est la balise javac:

<?xml version="1.0"?>
<project name="test-project" default="main" basedir=".">
  <!-- Sets variables which can later be used. -->
  <!-- The value of a property is accessed via ${} -->
  <property name="src.dir" location="src" />
  <property name="build.dir" location="bin" />
  <property name="dist.dir" location="dist" />
  <property name="docs.dir" location="docs" />

  <!-- Deletes the existing build, docs and dist directory-->
  <target name="clean">
    <delete dir="${build.dir}" />
    <delete dir="${docs.dir}" />
    <delete dir="${dist.dir}" />
  </target>

  <!-- Creates the  build, docs and dist directory-->
  <target name="makedir">
    <mkdir dir="${build.dir}" />
    <mkdir dir="${docs.dir}" />
    <mkdir dir="${dist.dir}" />
  </target>

  <!-- Compiles the java code (including the usage of library for JUnit -->
  <target name="compile" depends="clean, makedir">
    <javac srcdir="${src.dir}" destdir="${build.dir}">
    </javac>
  </target>

  <!-- Creates Javadoc -->
  <target name="docs" depends="compile">
    <javadoc packagenames="src" sourcepath="${src.dir}" destdir="${docs.dir}">
      <!-- Define which files / directory should get included, we include all -->
       <fileset dir="${src.dir}">
                <include name="**" />
           </fileset>
    </javadoc>
  </target>

  <!--Creates the deployable jar file  -->
  <target name="jar" depends="compile">
    <jar destfile="${dist.dir}test-project1.jar" basedir="${build.dir}">
      <manifest>
        <attribute name="Main-Class" value="test.Main" />
      </manifest>
    </jar>
  </target>

  <target name="main" depends="compile, jar, docs">
    <description>Main target</description>
  </target>

</project>