title: How can i add extra flags while running make?
body: <p>when I run <code>make</code>, how can i add some extra flags?</p>
  
  <p>seems like:</p>
  
  <pre><code>make CXXFLAGS="-pg" # will substitute original flags
  </code></pre>
  
  <p>and:</p>
  
  <pre><code>make CXXFLAGS+="-pg" # does not work either
  </code></pre>