title: cmake invalid numeric argument '/Wextra'
body: <p>Windows XP Pro 32bit</p>
  
  <p>Visual studio 2008 VC Express edition.</p>
  
  <p>I have installed cmake and created the CMakeLists.txt and I want to cross-platform for Linux/windows.</p>
  
  <p>Everything works ok for running on linux. So I copied my source directory as I am doing out of source building to my windows xp machine.</p>
  
  <p>I used the cmake-GUI to configure/generate the solution files. Everything ok there.</p>
  
  <p>However, when I opened the solution file and selected build from menu I got the following error.</p>
  
  <pre><code>cl : Command line error D8021 : invalid numeric argument '/Wextra'
  </code></pre>
  
  <p>Not sure really where to start looking to solve this error. If any one can point me in the right direction.</p>
  
  <p>Many thanks for any suggestions,</p>