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/*
 value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=35259437a7b13f8573f407c39e8c2c0308123a37'>root</a>/<a href='/guix/log/gnu?id=35259437a7b13f8573f407c39e8c2c0308123a37'>gnu</a>/<a href='/guix/log/gnu/packages?id=35259437a7b13f8573f407c39e8c2c0308123a37'>packages</a>/<a href='/guix/log/gnu/packages/tmux.scm?id=35259437a7b13f8573f407c39e8c2c0308123a37'>tmux.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/tmux.scm?id=35259437a7b13f8573f407c39e8c2c0308123a37&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-03-12 22:41:31 +0300'>2019-03-12</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=e80a809f1fca1bc8580a9ab24fc071b822f65e7e'>gnu: Add tmux-xpanes.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmux-xpanes): New variable.
</span></span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2019-02-14 18:16:07 +0100'>2019-02-14</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=66377fdced522d2798ce6846f1b035a7f20ab574'>gnu: tmuxifier: Don't use unstable tarball.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmuxifier)[source]: Use GIT-FETCH and
GIT-FILE-NAME.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-02-14 18:16:07 +0100'>2019-02-14</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=7bef8fd5cf849ca3732e03632f40fa253599ae0a'>gnu: tmux-themepack: Use GIT-* helpers, not NAME.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmux-themepack)[version]: Use GIT-VERSION.
[source]: Hard-code NAME.  Use GIT-FILE-NAME.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-10-19 03:18:57 +0200'>2018-10-19</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=2c0a3ed1f98e81c6c2f828c488ec7318181de539'>gnu: tmux: Update to 2.8.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmux): Update to 2.8.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-04-14 23:08:42 -0400'>2018-04-14</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=d2dd939e68370c7042a3ca3e6e644ce8d3f29e81'>gnu: tmux: Update to 2.7.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmux): Update to 2.7.
</span></span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2017-10-15 21:37:51 -0400'>2017-10-15</span></td><td><a href='/guix/commit/gnu/packages/tmux.scm?id=8de5ca028864d60d6bb6a60454fe491a6d194341'>gnu: tmux: Update to 2.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tmux.scm (tmux): Update to 2.6.
</span></span></td><td>Leo Famulari</td></tr>