title: How to detect sse availability in CMake
body: <p>In a CMakeLists.txt file, is there a way to detect the highest level of SSE available, and save it to CMAKE_CXX_FLAGS? In other words, I'd like to be able to write something like:</p>
  
  <pre><code>FindSSE()  # defines SSE_FLAGS
  set(CMAKE_CXX_FLAGS ${SSE_FLAGS})
  </code></pre>
  
  <p>For example, if the platform supports up to SSE level 3, then FindSSE() would set SSE_FLAGS to -msse3.</p>