Include a simple ant build file for the platform.jar part of the source. The next 
upstream version should already include this.

Index: libjna-java-3.2.7/pom.xml
===================================================================
--- libjna-java-3.2.7.orig/pom.xml	2011-05-22 20:06:42.104338432 +0100
+++ libjna-java-3.2.7/pom.xml	2011-05-22 20:08:00.283504785 +0100
@@ -33,6 +33,7 @@
               <tasks>
                 <!--<ant dir="." target="dist" />-->
                 <attachArtifact file="dist/jna.jar" />
+                <attachArtifact file="dist/platform.jar" />
                 <attachArtifact file="dist/src-mvn.zip" classifier="sources" type="jar"/>
               </tasks>
             </configuration>
@@ -64,4 +65,4 @@
       <url>http://download.java.net/maven/2/</url>
     </pluginRepository>
   </pluginRepositories>
-</project>
\ No newline at end of file
+</project>
Index: libjna-java-3.2.7/contrib/platform/build.xml
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ libjna-java-3.2.7/contrib/platform/build.xml	2011-06-03 18:23:26.431989502 +0100
@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project name="platform" default="jar" basedir=".">
+
+  <property name="src" location="src"/>
+  <property name="build" location="build"/>
+  <property name="dist"  location="../../build/"/>
+
+  <path id="classpath">
+    <fileset dir="${dist}" includes="jna.jar"/>
+  </path>
+
+  <target name="init">
+    <mkdir dir="${build}"/>
+  </target>
+
+  <target name="compile" depends="init" description="compile the source " >
+    <javac srcdir="${src}" destdir="${build}" classpathref="classpath"/>
+  </target>
+
+  <target name="jar" depends="compile" description="jar" >
+    <jar jarfile="${dist}/jna-platform.jar" basedir="${build}"/>
+  </target>
+
+  <target name="javadoc">
+    <!-- we don't build the javadoc for now, this should all 
+         be sorted in the next upstream release. -->
+  </target>
+
+  <target name="clean" description="clean" >
+    <delete dir="${build}"/>
+    <delete file="${dist}/jna-platform.jar"/>
+  </target>
+</project>
+