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"/>
>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=9c1697020912ac24ff6be7eb6591314fdb74fc07'>root</a>/<a href='/guix/log/gnu?id=9c1697020912ac24ff6be7eb6591314fdb74fc07'>gnu</a>/<a href='/guix/log/gnu/home.scm?id=9c1697020912ac24ff6be7eb6591314fdb74fc07'>home.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/home.scm?id=9c1697020912ac24ff6be7eb6591314fdb74fc07&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-03-20 09:14:23 +0400'>2023-03-20</span></td><td><a href='/guix/commit/gnu/home.scm?id=1f36534c7e8f2325bff4df5d37ecc811dc63fc38'>home: 'home-environment-with-provenance' uses the HE location info.</a><span class='msg-avail'>...</span></td><td>Sergey Trofimov</td></tr>
<tr><td><span title='2023-03-13 16:41:34 +0400'>2023-03-13</span></td><td><a href='/guix/commit/gnu/home.scm?id=377c8143e7cd5e3bf3e1e8d53ba443f91c88239c'>home: Export home-environment-packages.</a><span class='msg-avail'>...</span></td><td>Sergey Trofimov</td></tr>
<tr><td><span title='2022-08-19 18:55:41 +0300'>2022-08-19</span></td><td><a href='/guix/commit/gnu/home.scm?id=e60ba7eb6dd3d5847f7111f1a2ea33492b12cbc8'>home: Fix docstring.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>
<tr><td><span title='2022-08-01 00:02:04 +0200'>2022-08-01</span></td><td><a href='/guix/commit/gnu/home.scm?id=61db74a687e36e842077c5c2f4b2e2c7afcd814a'>home: Add 'home-generation-base'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-07-17 02:00:00 +0200'>2022-07-17</span></td><td><a href='/guix/commit/gnu/home.scm?id=670818a4049edb8a77a5b596fbc7558bde57165c'>Revert "home: Add 'home-generation-base'."</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-07-23 00:39:55 +0200'>2022-07-23</span></td><td><a href='/guix/commit/gnu/home.scm?id=5df8f7802e8b45855e8f84830677001dc631e4f7'>home: Add 'home-generation-base'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-19 23:39:55 +0100'>2021-12-19</span></td><td><a href='/guix/commit/gnu/home.scm?id=ed818c66d371656c869f43d7a7cbbcfba2df647b'>home: Add gexp-compiler for home-environments.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>
<tr><td><span title='2021-10-09 19:24:18 +0300'>2021-10-09</span></td><td><a href='/guix/commit/gnu/home.scm?id=0e8d2df0f1a4ab25c482e1c427c54e19903e62f3'>Move (gnu home-services) to (gnu home services).</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2021-10-08 15:36:18 +0300'>2021-10-08</span></td><td><a href='/guix/commit/gnu/home.scm?id=ba8ddb348045f81f061a1c7f51c0f7c2b0024e71'>gnu: Move (gnu home-services) to (gnu home services).</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2021-09-09 20:26:51 +0300'>2021-09-09</span></td><td><a href='/guix/commit/gnu/home.scm?id=994c66bf846774da5104537ef1037d6a5bc56995'>gnu: home: Add doc comment about the module.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>
<tr><td><span title='2021-09-09 20:26:50 +0300'>2021-09-09</span></td><td><a href='/guix/commit/gnu/home.scm?id=7fcc64253c2c48fee96f7925453161eb2b3a709e'>home: Add home-environment.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>