Don't unzip the sources which were bundled originally. Guix strips them from
the source and uses pre-build packages.

Taken from https://anonscm.debian.org/viewvc/pkg-java/trunk/libxerces2-java/debian/patches/02_build_dont_unzip.patch?revision=14507

Index: b/build.xml
===================================================================
--- a/build.xml
+++ b/build.xml
@@ -247,7 +247,7 @@
     <copy file="${src.dir}/org/apache/xerces/impl/xpath/regex/message.properties"
       tofile="${build.src}/org/apache/xerces/impl/xpath/regex/message_en.properties"/>
 
-    <!-- now deal with API's:  -->
+    <!-- not needed for Debian
     <unzip src="${src.apis.zip}" dest="${build.src}">
         <patternset
             includes="org/xml/sax/** 
@@ -270,6 +270,7 @@
                 org/w3c/dom/xpath/**"
         />
     </unzip>
+    -->
     
     <!-- substitute tokens as needed -->
     <replace file="${build.dir}/src/org/apache/xerces/impl/Version.java" 
@@ -1232,7 +1233,7 @@
     <replace file="${build.dir}/src/org/apache/xerces/parsers/AbstractSAXParser.java"
              token="return (fConfiguration instanceof XML11Configurable);" value="return false;"/>
  
-    <!-- now deal with API's:  -->
+    <!-- not needed for Debian
     <unzip src="${src.apis.zip}" dest="${build.src}">
         <patternset
             includes="org/xml/sax/** 
@@ -1255,7 +1256,7 @@
                 org/w3c/dom/xpath/**"
         />
     </unzip>
-
+    -->
 
     <!-- substitute tokens as needed -->
     <replace file="${build.dir}/src/org/apache/xerces/impl/Version.java"