title: CMake -G Ninja on Windows specify x64
body: <p>I am using CMake on Windows with Ninja generator</p>
  
  <pre><code>cmake -G Ninja ..
  </code></pre>
  
  <p>This uses the default Windows x86 toolchain.
  How to specify x64 using the Ninja generator?</p>
  
  <p>PS: I know how to generate x64 with Visual Studio</p>
  
  <pre><code>cmake -G "Visual Studio 12 2013 Win64 ..
  </code></pre>