title: How to turn on STL backward compatability?
body: <p>I am trying to compile something that uses Google's sparsehash include files.</p>
  
  <pre><code>libs/include/google/dense_hash_map:93:60: error: ext/hash_fun.h: No such file or directory
  ^Cmake: *** [all] Interrupt
  </code></pre>
  
  <p>I know that hash_fun.h exists in /usr/include/c++/4.3/backward/hash_fun.h.
  I am just not sure how to make google sparse hash use it. Any idea? I would really like to avoid tampering with either the google files or the /usr/include files. I had already to use -Wno-deprecated for removing an error about using an old STL include file, but I am pretty sure there is a way to get #include  be recognized when using newer versions of STL.</p>