This patch eliminates the need for providing "xjavac", which saves building a
package for the unmaintained "xerces-tools".

Taken from https://anonscm.debian.org/viewvc/pkg-java/trunk/libxerces2-java/debian/patches/01_xjavac_taskdef.patch?revision=14507

Index: b/build.xml
===================================================================
--- a/build.xml
+++ b/build.xml
@@ -39,7 +39,7 @@
   <property name="tools.dir" value="./tools"/>
 
   <!-- enable compilation under JDK 1.4 and above -->
-  <taskdef name="xjavac" classname="org.apache.xerces.util.XJavac">
+  <taskdef name="xjavac" classname="org.apache.tools.ant.taskdefs.Javac">
     <classpath>
       <pathelement location="${tools.dir}/bin/xjavac.jar"/>
     </classpath>
@@ -291,7 +291,7 @@
            source="${javac.source}"
            target="${javac.target}"
            classpath="${build.dir}/classes:${tools.dir}/${jar.apis}:${tools.dir}/${jar.resolver}:${tools.dir}/${jar.serializer}"
-           debug="${debug}"
+           debug="${debug}" nowarn="true"
            debuglevel="${debuglevel}"
            deprecation="${deprecation}"
            optimize="${optimize}"
@@ -359,7 +359,7 @@
            source="${javac.source}"
            target="${javac.target}"
            classpath="${build.dir}/classes:${tools.dir}/${jar.apis}"
-           debug="${debug}"
+           debug="${debug}" nowarn="true"
            debuglevel="${debuglevel}"
            includeAntRuntime="false"
            includeJavaRuntime="true"/>
@@ -379,7 +379,7 @@
            source="${javac.source}"
            target="${javac.target}"
            classpath="${tools.dir}/${jar.apis}:${build.dir}/classes:./tools/junit.jar"
-           debug="${debug}"
+           debug="${debug}" nowarn="true"
            debuglevel="${debuglevel}"
            includeAntRuntime="false"
            includeJavaRuntime="true"/>
ath'>path: <a href='/guix/log/?id=9b18e5696931fcb858bf0531670b2ded7c2b4505'>root</a>/<a href='/guix/log/README?id=9b18e5696931fcb858bf0531670b2ded7c2b4505'>README</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/README?id=9b18e5696931fcb858bf0531670b2ded7c2b4505&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-10-23 12:57:20 -0400'>2020-10-23</span></td><td><a href='/guix/commit/README?id=b5aaa3a4fb985d21e21e2a67f48b52f13ebd4728'>doc: Update README.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-10-22 22:47:54 -0400'>2020-10-22</span></td><td><a href='/guix/commit/README?id=503d2bfde08f9bf97bbf430516d2f19faedd4319'>README: Refer to the manual for building from Git.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-06-02 18:55:53 +0200'>2020-06-02</span></td><td><a href='/guix/commit/README?id=c75a80189fc19f6ff8b4c82d1d1801be6763b6d2'>doc: Update README to refer to the manual.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-09 23:04:14 +0100'>2019-11-09</span></td><td><a href='/guix/commit/README?id=0758a70cc008171f31c848128deca9803536fe60'>doc: Mention value /var to localstatedir option.</a><span class='msg-avail'>...</span></td><td>zimoun</td></tr>
<tr><td><span title='2019-09-04 23:41:07 +0200'>2019-09-04</span></td><td><a href='/guix/commit/README?id=f475c6e53e5b6912cc45663d50f1d03dadfb60b8'>doc: Update 'README'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>