title: cmake: Selecting a generator within CMakeLists.txt
body: <p>I would like to <strong>force CMake</strong> to use the "Unix Makefiles" <strong>generator</strong> from within CMakeLists.txt.</p>
  
  <p><strong>This is the command I use now.</strong></p>
  
  <pre><code>cmake -G "Unix Makefiles" .
  </code></pre>
  
  <p><strong>I would like it to be this.</strong></p>
  
  <pre><code>cmake .
  </code></pre>
  
  <p>When running on windows with VC installed and a custom tool-chain.</p>
  
  <p>I would expect to be-able to set the generator in the <code>CMakeLists.txt</code> file.</p>
  
  <p><strong>Maybe something like this.</strong></p>
  
  <pre><code>set(CMAKE_GENERATOR "Unix Makefiles")
  </code></pre>