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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</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=461602d07c8da0e29bae392270f4ef3fd4f7fffb'>root</a>/<a href='/guix/log/gnu?id=461602d07c8da0e29bae392270f4ef3fd4f7fffb'>gnu</a>/<a href='/guix/log/gnu/packages?id=461602d07c8da0e29bae392270f4ef3fd4f7fffb'>packages</a>/<a href='/guix/log/gnu/packages/python.scm?id=461602d07c8da0e29bae392270f4ef3fd4f7fffb'>python.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/packages/python.scm?id=461602d07c8da0e29bae392270f4ef3fd4f7fffb&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-07-20 10:11:33 +0200'>2023-07-20</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=60b1a230656386994bcfa5f6f7be72c2376341ed'>gnu: python: Support native build on the Hurd.</a><span class='msg-avail'>...<span class='msg-tooltip'>Running "test_concurrent_futures" and "test_venv" freeze the Hurd.  Tests
"test_multiprocessing_forkserver" and "test_multiprocessing_spawn" run over
10mins. Debian simply skips all tests on the Hurd.

* gnu/packages/python.scm (python-3.10)[arguments]: When building for the
Hurd, add hanging and failing to #:make-flags's --exclude flag.  Also, add
'disable-multi-processing' phase to avoid compileall.py hang during install.
</span></span></td><td>Janneke Nieuwenhuizen</td></tr>
<tr><td><span title='2023-06-17 14:38:32 +0200'>2023-06-17</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=ff690faf66d8f37ee6b679fcb7cf37e369624ee3'>gnu: Use target-hurd?, system-hurd? instead of hurd-target?, hurd-system?.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/hurd.scm (hurd-target?): Remove.
(hurd-system?): Move to...
* guix/utils.scm (system-hurd?): ...here.
* gnu/packages/*: Update all users, removing (gnu packages hurd) include where
now unused.
</span></span></td><td>Janneke Nieuwenhuizen</td></tr>
<tr><td><span title='2023-04-14 23:37:05 -0400'>2023-04-14</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=97e37a8a79d8f430f3023ebec49277b9cb65468a'>gnu: wrap-python3: Replace assoc-ref call with gexp variable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/python.scm (wrap-python3) [arguments]: Replace assoc-ref call
with gexp variable in builder.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2023-03-09 22:33:05 +0100'>2023-03-09</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=af916f3f8b5e1191cdcc95dded1e376f51ad9e9b'>gnu: python-wrapper: Refer to the target Python when cross-compiling.</a><span class='msg-avail'>...<span class='msg-tooltip'>Previously, "guix build python-wrapper --target=aarch64-linux-gnu" would
return a wrapper that symlinks the native programs (e.g., 'python3' for
x86_64-linux) instead of the target programs.

* gnu/packages/python.scm (wrap-python3)[arguments]: Use gexps.  Use
'this-package-input' to refer to Python when cross-compiling.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-03-02 10:55:08 +0000'>2023-03-02</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=7df09ee0ab3e7962ef27859ce87e06a323059284'>Merge remote-tracking branch 'savannah/master' into core-updates</a><span class='msg-avail'>...<span class='msg-tooltip'>Conflicts:
	gnu/local.mk
	gnu/packages/autotools.scm
	gnu/packages/cmake.scm
	gnu/packages/gnuzilla.scm
	gnu/packages/haskell.scm
	gnu/packages/pdf.scm
	gnu/packages/python-xyz.scm
	gnu/packages/samba.scm
	gnu/packages/tex.scm
	gnu/packages/tls.scm
	gnu/packages/wxwidgets.scm
</span></span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2023-02-25 00:00:32 +0100'>2023-02-25</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=7dbd73a329d9918711f45c8090a3a92520836211'>gnu: python: Remove input labels.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/python.scm (python-3.9)[native-inputs]: Remove labels.
(python2-minimal)[inputs]: Likewise.
(python-minimal)[inputs]: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-01-30 12:39:40 +0200'>2023-01-30</span></td><td><a href='/guix/commit/gnu/packages/python.scm?id=4cf1acc7f3033b50b0bf19e02c9f522d522d338c'>Merge remote-tracking branch 'origin/master' into core-updates</a><span class='msg-avail'>...<span class='msg-tooltip'> Conflicts:
	doc/guix.texi
	gnu/local.mk
	gnu/packages/admin.scm
	gnu/packages/base.scm
	gnu/packages/chromium.scm
	gnu/packages/compression.scm
	gnu/packages/databases.scm
	gnu/packages/diffoscope.scm
	gnu/packages/freedesktop.scm
	gnu/packages/gnome.scm
	gnu/packages/gnupg.scm
	gnu/packages/guile.scm
	gnu/packages/inkscape.scm
	gnu/packages/llvm.scm
	gnu/packages/openldap.scm
	gnu/packages/pciutils.scm
	gnu/packages/ruby.scm
	gnu/packages/samba.scm
	gnu/packages/sqlite.scm
	gnu/packages/statistics.scm
	gnu/packages/syndication.scm
	gnu/packages/tex.scm
	gnu/packages/tls.scm
	gnu/packages/version-control.scm
	gnu/packages/xml.scm
	guix/build-system/copy.scm
	guix/scripts/home.scm
</span></span></td><td>Efraim Flashner</td></tr>