Enable configuralbe mergemanifest.enabled again. It's reverted on recent refactoring

build/android/ant/apk-codegen.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!--
     Copyright (C) 2005-2008 The Android Open Source Project
 
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0
 
@@ skipping 45 matching lines @@
   <script language="javascript">
     var before = project.getProperty("ADDITIONAL_RES_PACKAGES");
     project.setProperty("project.library.packages", before.replaceAll(" ", ";"));
   </script>
 
   <path id="project.library.manifest.file.path">
     <filelist files="${LIBRARY_MANIFEST_PATHS}"/>
   </path>
 
   <!-- manifest merger default value -->
-  <property name="manifestmerger.enabled" value="false" />
+  <condition property="manifestmerger.enabled"
+      value="false"
+      else="true">
+    <equals arg1="${LIBRARY_MANIFEST_PATHS}" arg2="" />
+  </condition>
 
   <property name="resource.absolute.dir" value="${RESOURCE_DIR}"/>
 
   <property name="manifest.file" value="${ANDROID_MANIFEST}" />
   <property name="manifest.abs.file" location="${manifest.file}" />
 
   <!-- Intermediate files -->
   <property name="resource.package.file.name" value="${APK_NAME}.ap_" />
 
   <property name="aapt.ignore.assets" value="" />
@@ skipping 26 matching lines @@
               ignoreAssets="${aapt.ignore.assets}"
               binFolder="${out.absolute.dir}"
               proguardFile="${out.absolute.dir}/proguard.txt">
           <res path="${out.res.absolute.dir}" />
           <res path="${resource.absolute.dir}" />
       </aapt>
 
       <touch file="${STAMP}" />
   </target>
 </project>