title: Suppress make rule error output
body: <p>I have an rule that creates a directory</p>
  
  <pre><code>bin:
      -mkdir $@
  </code></pre>
  
  <p>However after the first time the directory has been generated, I receive this output:</p>
  
  <pre><code>mkdir bin
  mkdir: cannot create directory `bin': File exists
  make: [bin] Error 1 (ignored)
  </code></pre>
  
  <p>Is there some way I can only run the rule if the directory doesn't exist, or suppress the output when the directory already exists?</p>