title: cmake keeps adding the std=gnu++11 option
body: <p>I'm trying to compile a project in <strong>C++</strong> using <code>cmake</code>, and in the page of the project they tell me that it will crash if I don't add the standard 98. (I'm on a mac)
  I've tried all I found on the internet and I could manage to make the <code>cmake</code> use the option <code>-std=c++98</code> but it also adds <code>-DNDEBUG -std=gnu++11</code>.  (I saw it using the make <code>VERBOSE=1</code> option)</p>
  <p>I would like to get rid of that. Using the <code>--trace</code> option I could see that the option is set in a file which is in the cellar folder, that is, is something that has to do with <code>cmake</code> itself and not in the <code>CMakeList.txt</code> file im using.</p>
  <p>How can I solve this problem?</p>
  <p>If it can help the code I'm trying to compile is this:
  <a href="https://github.com/sknepneklab/SAMoS" rel="noreferrer">SAMoS</a></p>
  <p>Thank you.</p>
  <p><strong>UPDATE:</strong></p>
  <p>with the <code>--trace</code> option I was able to see that the <code>-std=gnu++11</code> option was selected in the file:</p>
  <p><code>/usr/local/Cellar/cmake/3.9.4.1/share/cmake/Modules/Compiler/GNU-CXX.cmake</code>
  which can be seen here <a href="https://github.com/Kitware/CMake/blob/master/Modules/Compiler/GNU-CXX.cmake" rel="noreferrer">GNU-CXX.cmake</a></p>
  <p>If I eddit that file in a way that every if sets the option to <code>-std=c++98</code> then, the cmake complains giving me the next error:</p>
  <blockquote>
  <p>CMake Error in src/CMakeLists.txt:</p>
  <p>The compiler feature &quot;cxx_nullptr&quot; is not known to CXX compiler</p>
  <p>&quot;GNU&quot;</p>
  <p>version 7.2.0.</p>
  </blockquote>
  <p>I don't know what else can I try...</p>