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"/>
xt' type='search' size='10' name='q' value=''/>
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</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=a9ee95aec119601332875d9c4becef2331780fee'>root</a>/<a href='/guix/log/etc?id=a9ee95aec119601332875d9c4becef2331780fee'>etc</a>/<a href='/guix/log/etc/completion?id=a9ee95aec119601332875d9c4becef2331780fee'>completion</a>/<a href='/guix/log/etc/completion/zsh?id=a9ee95aec119601332875d9c4becef2331780fee'>zsh</a>/<a href='/guix/log/etc/completion/zsh/_guix?id=a9ee95aec119601332875d9c4becef2331780fee'>_guix</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/etc/completion/zsh/_guix?id=a9ee95aec119601332875d9c4becef2331780fee&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-10-24 20:17:05 +0200'>2021-10-24</span></td><td><a href='/guix/commit/etc/completion/zsh/_guix?id=55f6d9e818512b4e3e4adacfa99deb201b6854be'>etc: completion: Filter gratuitous spaces from available packages.</a><span class='msg-avail'>...<span class='msg-tooltip'>Tested with:

  guix environment --{ad-hoc,pure} zsh guix bash-completion coreutils -- zsh
  % fpath=(~/guix/etc/completion/zsh $fpath)
  % autoload -U compinit; compinit

* etc/completion/zsh/_guix (_guix_list_available_packages): Remove spaces.

Co-authored-by: Tobias Geerinckx-Rice &lt;me@tobias.gr&gt;
</span></span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2021-08-28 17:57:50 +0200'>2021-08-28</span></td><td><a href='/guix/commit/etc/completion/zsh/_guix?id=a8dd285d5a0670abf124a721e6ba94da045b24ba'>zsh completion: Add missing commands and arguments.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/completion/zsh/_guix (_guix_install, _guix_remove, _guix_upgrade):
  New functions.
  (_guix_build, _guix_challenge, _guix_download, _guix_environment,
  _guix_packages, _guix_gc, _guix_hash, _guix_lint, _guix_package,
  _guix_publish, _guix_pull, _guix_refresh, _guix_size, _guix_system):
  Add some of the missing arguments.
  (_guix_cmds): Add missing commands.

Co-authored-by: Brice Waegeneire &lt;brice@waegenei.re&gt;
</span></span></td><td>Noah Evans</td></tr>
<tr><td><span title='2021-02-17 10:52:28 +0100'>2021-02-17</span></td><td><a href='/guix/commit/etc/completion/zsh/_guix?id=ee2a5da80a9bda25542c00a7a35a9ddddcbd58af'>scripts: system: Remove 'vm-image' command.</a><span class='msg-avail'>...<span class='msg-tooltip'>Remove the 'vm-image' command that has been superseded by the 'image'
command.

* gnu/system/vm.scm (system-qemu-image): Remove it.
* guix/scripts/system.scm (system-derivation-for-action): Mark 'vm-image'
command as deprecated and use the image API to produce the VM image.
(perform-action, show-help): Adapt accordingly.
* tests/guix-system.sh: Ditto.
* doc/guix.texi (Invoking guix system,
Running Guix in a VM): Ditto.
* etc/completion/fish/guix.fish: Ditto.
* etc/completion/zsh/_guix: Ditto.
</span></span></td><td>Mathieu Othacehe</td></tr>