title: Remove a flag from C++FLAGS in Makefile?
body: <p>I've got a Makefile that includes another makefile that sets a lot of defaults. I can't edit the included makefile and I'd like to change the value of C++FLAGS in my makefile even though it is set in the included makefile. Specifically, I'd like to remove the optimization flag from C++FLAGS whenever debug=1. </p>
  
  <p>I tried the following:</p>
  
  <pre><code>C++FLAGS=$(filter-out -O3,$(C++FLAGS))
  </code></pre>
  
  <p>Which fails with the following error:</p>
  
  <pre><code>Recursive variable `C++FLAGS' references itself (eventually).  Stop.
  </code></pre>
  
  <p>It seems like doing something like this should be possible, anybody know the secret?</p>