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"/>
n>
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</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=bc69ad7b364620f2820203b9adef356a7f0515f7'>root</a>/<a href='/guix/log/gnu?id=bc69ad7b364620f2820203b9adef356a7f0515f7'>gnu</a>/<a href='/guix/log/gnu/build?id=bc69ad7b364620f2820203b9adef356a7f0515f7'>build</a>/<a href='/guix/log/gnu/build/secret-service.scm?id=bc69ad7b364620f2820203b9adef356a7f0515f7'>secret-service.scm</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/gnu/build/secret-service.scm?id=bc69ad7b364620f2820203b9adef356a7f0515f7&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-09-29 21:56:27 +0200'>2020-09-29</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=d5366500ec1aeecad6fc292b195088e30aa715fd'>secret-service: Add proper logging procedure and log to syslog.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-29 21:56:27 +0200'>2020-09-29</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=59261a22f9819b1fdf797ffba17af17d385d6c92'>services: secret-service: Add initial client/server handshake.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-29 21:56:27 +0200'>2020-09-29</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=f9090015c58e6f47be74fe6116ef10a90378a899'>secret-service: Fix file port leak in 'secret-service-send-secrets'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-29 21:56:27 +0200'>2020-09-29</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=4d047853da76dc5fa5dd50ecb750c861342ef47b'>secret-service: Add a timeout when waiting for a client.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-29 21:56:26 +0200'>2020-09-29</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=118b6dbb46ff3376db7467301fe59673c042d220'>secret-service: Clarify the origin of messages.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-01 16:06:38 +0200'>2020-09-01</span></td><td><a href='/guix/commit/gnu/build/secret-service.scm?id=ec32d4f291b3cc039a99f8090b6c2b2444be5a83'>services: Add secret-service-type.</a><span class='msg-avail'>...</span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>