title: Use post-build-scripts in buildroot
body: <p>i use buildroot to build my own rootfs and use post-build.sh to customize it.</p>
  
  <p>In concrete i create a textfile in /opt with   </p>
  
  <pre><code>touch $TARGET_DIR/opt/testfile01.txt
  </code></pre>
  
  <p>and run the make command. I checked the out coming rootfs and testfile01.txt is in /opt. Everyting ok.</p>
  
  <p>Then I change the content of my post-build-sh to</p>
  
  <pre><code>touch $TARGET_DIR/opt/testfile02.txt
  </code></pre>
  
  <p>and run the make command again. </p>
  
  <p>The behaviour i observe is that both files (testfile01 and testfile02) exists in rootfs after the second make.
  Also removing rootfs and than run make command do not change this behavior.</p>
  
  <p>In buildroot manual is written that there is no need for a full rebuild after make changes in post-build scripts.</p>
  
  <p>How can in change this behaviour?</p>
  
  <p>Thanks for helping</p>
  
  <p>Edit: buildroot-2018.02.2, Ubuntu 18.04 LTS</p>