title: autoconf & c++ & obsolete headers
body: <p>Some code I have runs into the following with modern C++. Of course, there's a better way to express this in modern C++. Question is, how to use automake to set a CPP macro for conditionalization?</p>
  
  <pre><code>In file included from /usr/include/c++/4.4/ext/hash_map:60,
                   from grapes.hpp:54,
                   from broadmerger.hpp:22,
                   from broadmerger.cpp:16:
  /usr/include/c++/4.4/backward/backward_warning.h:28: error: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated.
  </code></pre>