Based on https://anonscm.debian.org/viewvc/pkg-java/trunk/libxerces2-java/debian/patches/03_bootclasspath.patch?revision=14509, adopted for guix

--- xerces-2_11_0/build.xml.orig	2010-11-26 21:42:11.000000000 +0100
+++ xerces-2_11_0/build.xml	2017-03-28 14:04:41.946606996 +0200
@@ -290,13 +290,14 @@
            destdir="${build.dest}"
            source="${javac.source}"
            target="${javac.target}"
-           classpath="${build.dir}/classes:${tools.dir}/${jar.apis}:${tools.dir}/${jar.resolver}:${tools.dir}/${jar.serializer}"
+           classpath="${build.dir}/classes:${jar.jaxp}:${jar.apis-ext}:${jar.resolver}"
            debug="${debug}" nowarn="true"
            debuglevel="${debuglevel}"
            deprecation="${deprecation}"
            optimize="${optimize}"
            includeAntRuntime="false"
-           includeJavaRuntime="false"
+           includeJavaRuntime="true"
+           bootclasspath="${jar.jaxp}:${jar.apis-ext}:${jar.resolver}"
            excludes="org/xml/sax/** 
                 javax/xml/**
                 org/w3c/dom/*
@@ -1451,13 +1452,14 @@
                destdir="${build.dest}"
                source="${javac.source}"
                target="${javac.target}"
-               classpath="${build.dir}/classes:${tools.dir}/${jar.apis}:${tools.dir}/${jar.resolver}:${tools.dir}/${jar.serializer}"
+               classpath="${build.dir}/classes:${jar.jaxp}:${jar.apis-ext}:${jar.resolver}"
                debug="${debug}"
                debuglevel="${debuglevel}"
                deprecation="${deprecation}"
                optimize="${optimize}"
                includeAntRuntime="false"
-               includeJavaRuntime="false"
+               includeJavaRuntime="true"
+               bootclasspath="${jar.jaxp}:${jar.apis-ext}:${jar.resolver}"
                excludes="org/xml/sax/** 
                     javax/xml/**
                     org/w3c/dom/*
a href='/guix/log/?id=27bcdfcd65c0333abd2cd7cb412053b78eaaa70c'>root</a>/<a href='/guix/log/nix?id=27bcdfcd65c0333abd2cd7cb412053b78eaaa70c'>nix</a>/<a href='/guix/log/nix/libutil?id=27bcdfcd65c0333abd2cd7cb412053b78eaaa70c'>libutil</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/nix/libutil?id=27bcdfcd65c0333abd2cd7cb412053b78eaaa70c&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-11-29 15:54:20 +0100'>2019-11-29</span></td><td><a href='/guix/commit/nix/libutil?id=b6b014bf42f68fcb71d37204328babb81e0e0855'>daemon: 'pathExists' uses 'statx' when available.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libutil/util.cc (pathExists) [HAVE_STATX]: New code.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-27 00:03:03 +0100'>2019-11-27</span></td><td><a href='/guix/commit/nix/libutil?id=fbecb5cddb2d36cc1a29dac3751b017fa531383c'>daemon: 'deletePath' uses 'statx' when available.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libutil/util.cc (_deletePath) [HAVE_STATX]: Use 'statx'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-08-30 01:33:45 +0200'>2019-08-30</span></td><td><a href='/guix/commit/nix/libutil?id=546a709f202024c8a5173ad372a87ddc1c284c63'>daemon: Don't reply on 'st_blocks'.</a><span class='msg-avail'>...<span class='msg-tooltip'>Ported by Ludovic Courtès &lt;ludo@gnu.org&gt;
from &lt;https://github.com/NixOS/nix/commit/a2c4fcd5e9782dc8d2998773380c7171ee53b813&gt;.

* nix/libstore/gc.cc (LocalStore::removeUnusedLinks): Use 'st.st_size'
instead of 'st.st_blocks * 512'.
* nix/libutil/util.cc (_deletePath): Likewise.
</span></span></td><td>Eelco Dolstra</td></tr>
<tr><td><span title='2018-12-16 16:28:07 +0100'>2018-12-16</span></td><td><a href='/guix/commit/nix/libutil?id=8327e733966cc4a93dfaadd1a761ca1088078baa'>daemon: Use unbranded phrases in comments and messages.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libstore/build.cc, nix/libstore/globals.cc,
nix/libstore/gc.cc, nix/libstore/local-store.cc,
nix/libstore/optimise-store.cc, nix/libstore/store-api.cc,
nix/libutil/archive.cc, nix/nix-daemon/nix-daemon.cc: Replace "Nix
store" by "store", and "Nix daemon" by "build daemon".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-10-02 23:08:30 +0200'>2018-10-02</span></td><td><a href='/guix/commit/nix/libutil?id=7eca7892014d173ff523417138b90aeff5b7dec1'>daemon: Remove "case hack" for nars.</a><span class='msg-avail'>...<span class='msg-tooltip'>This code has never been of any use in Guix.

* nix/libutil/archive.cc (useCaseHack): Remove.
(parse): Keep only the alternate branch in "if (useCaseHack)".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-08-18 11:31:28 +0200'>2017-08-18</span></td><td><a href='/guix/commit/nix/libutil?id=ed464f48efd80e6439441d7a9f6d0e7988fb1272'>nix: Remove unused function.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libutil/util.hh:
* nix/libutil/util.cc (decodeOctalEscaped): Remove unused and buggy function.
</span></span></td><td>Andy Wingo</td></tr>