Work with Java 10+.

Index: jffi/build.xml
--- jffi/build.xml.orig
+++ jffi/build.xml
@@ -151,8 +151,9 @@
 
   <target name="-do-compile" depends="-init">
     <mkdir dir="${build.classes.dir}"/>
+    <mkdir dir="${build.native.dir}"/>
     <!-- Compile the java code from ${src} into ${build} -->
-    <javac srcdir="${src.dir}" destdir="${build.classes.dir}" includeantruntime="false"/>
+    <javac srcdir="${src.dir}" destdir="${build.classes.dir}" includeantruntime="false" nativeHeaderDir="${build.native.dir}"/>
   </target>
 
   <target name="-compile-java" depends="-do-compile"/>
@@ -320,27 +321,10 @@
 
 
   <target name="-generate-version" depends="-init,-init-vars,-generate-version-source">
-    <javac target="${ant.build.javac.target}" destdir="${build.classes.dir}" srcdir="${build.dir}/java" includeantruntime="false"/>
+    <javac target="${ant.build.javac.target}" destdir="${build.classes.dir}" srcdir="${build.dir}/java" includeantruntime="false" nativeHeaderDir="${build.native.dir}"/>
   </target>
 
   <target name="-generate-native-headers" depends="-init-vars,-generate-version,-compile-java">
-    <mkdir dir="${build.native.dir}"/>
-    <mkdir dir="${build.classes.dir}"/>
-    <javac destdir="${build.native.dir}" nativeheaderdir="${build.native.dir}">
-      <src path="${src.dir}"/>
-      <src path="${build.dir}/java"/>
-      <include name="com/kenai/jffi/Foreign.java"/>
-      <include name="com/kenai/jffi/ObjectBuffer.java"/>
-      <include name="com/kenai/jffi/Version.java"/>
-    </javac>
-    <!--
-    <exec executable="javah" failonerror="true">
-      <arg line="-d ${build.native.dir}"/>
-      <arg line="-classpath ${build.classes.dir}"/>
-      <arg line="com.kenai.jffi.Foreign"/>
-      <arg line="com.kenai.jffi.ObjectBuffer"/>
-    </exec>
-    -->
   </target>
 
   <target name="-build-native-library" depends="-init-vars, -generate-native-headers, -generate-version">