title: Multiple Cmake_Prefix_Paths
body: <p>On a project I develop on, we're using cmake to compile our service. Currently, we need to get data for Qt from 3 different locations and I'm curious if there's a way to run one cmake command over three separate ones.</p>
  
  <p>What we currently use:</p>
  
  <pre><code>cmake -G "Visual Studio 12 2013" -DWITH_SERVER=1 -DCMAKE_PREFIX_PATH=C:\Qt\5.5\msvc2013\lib\cmake ..
  cmake -G "Visual Studio 12 2013" -DWITH_SERVER=1 -DCMAKE_PREFIX_PATH=C:\protobuf\src ..
  cmake -G "Visual Studio 12 2013" -DWITH_SERVER=1 -DCMAKE_PREFIX_PATH=C:\protobuf\cmake\build\Release ..
  </code></pre>
  
  <p>We've attempted to pass the same flag 3 times and separating the paths with <code>:</code> and <code>;</code>, but none seem to work as expected.</p>