title: Qt build fails due to missing std::isnan in Visual Studio 2012
body: <p>I'm trying to build Qt 5.2.0 from source using Visual Studio 2012. It is failing while compiling the following file:</p>
  
  <p><code>/qtdeclarative/src/qml/jsruntime/qv4value_p.h</code></p>
  
  <p>With the following error:</p>
  
  <p><code>191: error C2039: _isnan: is not a member of std</code></p>
  
  <p>Line 191 contains the following:</p>
  
  <p><code>return doubleValue() &amp;&amp; !std::isnan(doubleValue());</code></p>
  
  <p><a href="http://en.cppreference.com/w/cpp/numeric/math/isnan" rel="nofollow noreferrer">According to cppreference</a>, <code>std::isnan</code> should be defined in the header <code>cmath</code>, since C++11. The Qt header file does include this header. When I inspect <code>cmath</code> in Visual Studio, I cannot see a function named <code>isnan</code>.</p>
  
  <p>Am I right in concluding that VS2012 is missing this C++11 function? At first I thought I might have to enable C++11 support somehow, but according to <a href="https://stackoverflow.com/a/5121547/1227469">this answer</a> C++11 support is enabled by default. Given that <a href="http://qt-project.org/downloads" rel="nofollow noreferrer">binary downloads for Qt are available for VS2010 and VS2012</a>, clearly it is possible to build with the respective compilers. Is there something I am missing?</p>