title: How to tell scons to use MinGW instead of MSVC
body: <p>I'm trying to build the C++ port of zxing on Windows, but scons fails with:</p>
  
  <pre><code>cl : Command line error D8021 : invalid numeric argument '/Wextra'
  </code></pre>
  
  <p>I have both VS2010 and MinGW installed, and scons tries to use the MSVC compiler, even though the SConscript file assumes gcc and use gcc-specific parameters, which causes the error.</p>
  
  <p>How can I tell scons to use MinGW instead?</p>