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"/>
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</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=fc80efe1a0ea27e429e6b7bf467dd1f6aafe3ddf'>root</a>/<a href='/guix/log/tests?id=fc80efe1a0ea27e429e6b7bf467dd1f6aafe3ddf'>tests</a>/<a href='/guix/log/tests/guix-authenticate.sh?id=fc80efe1a0ea27e429e6b7bf467dd1f6aafe3ddf'>guix-authenticate.sh</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/tests/guix-authenticate.sh?id=fc80efe1a0ea27e429e6b7bf467dd1f6aafe3ddf&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-22 10:53:19 +0100'>2021-12-22</span></td><td><a href='/guix/commit/tests/guix-authenticate.sh?id=9ebc9ca070a21ba0aeb3f61202a8071bb250ccc8'>tests: Move keys into ./tests/keys/ and add a third ed25519 key.</a><span class='msg-avail'>...<span class='msg-tooltip'>The third key will be used in an upcoming commit.

Rename public keys to .pub.

* guix/tests/gnupg.scm (%ed25519-3-public-key-file): New variable.
(%ed25519-3-secret-key-file): New variable.
(%ed25519-2-public-key-file): Renamed from %ed25519bis-public-key-file.
(%ed25519-2-secret-key-file): Renamed from %ed25519bis-secret-key-file.
* tests/keys/ed25519-3.key: New file.
* tests/keys/ed25519-3.sec: New file.

Signed-off-by: Mathieu Othacehe &lt;othacehe@gnu.org&gt;
</span></span></td><td>Attila Lendvai</td></tr>
guix/commit/gnu/home/services/guix.scm?id=8d922504b22b81f99bf2dcbb9f15498ad513040a'>gnu: home: Add Guix channels service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/home/services/guix.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add guix.scm.
* doc/guix.texi: Add documentation for home-channels-service.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Reily Siegel</td></tr>