title: telling 'make' to ignore dependencies when the top target has been created
body: <p>I'm running the following kind of pipeline:</p>
  
  <pre><code>digestA: hugefileB hugefileC
      cat $^ &gt; $@
      rm $^
  
  hugefileB:
      touch $@
  
  hugefileC:
      touch $@
  </code></pre>
  
  <p>The targets <strong>hugefileB</strong> and <strong>hugefileC</strong> are very big and take a long time to compute (and need the power of Make). But once <strong>digestA</strong> has been created, there is no need to keep its dependencies: it deletes those dependencies to free up disk space.</p>
  
  <p>Now, if I invoke 'make' again, <strong>hugefileB</strong> and <strong>hugefileC</strong> will be rebuilt, whereas <strong>digestA</strong> is already ok.</p>
  
  <p>Is there any way to tell 'make' to avoid to re-comile the dependencies ?</p>
  
  <p>NOTE: I don't want to build the two dependencies inside the rules for 'digestA'.</p>