title: pthread_create not found in ubuntu
body: <p>I am trying to run cocos2d-x on Ubuntu. It shows this error:</p>
  
  <pre><code>-- Looking for IceConnectionNumber in ICE
  -- Looking for IceConnectionNumber in ICE - found
  -- Found X11: /usr/lib/x86_64-linux-gnu/libX11.so
  -- Found OpenGL: /usr/lib/x86_64-linux-gnu/libGL.so  
  -- Looking for include file pthread.h
  -- Looking for include file pthread.h - found
  -- Looking for pthread_create
  -- Looking for pthread_create - not found
  -- Looking for pthread_create in pthreads
  -- Looking for pthread_create in pthreads - not found
  -- Looking for pthread_create in pthread
  -- Looking for pthread_create in pthread - found
  -- Found Threads: TRUE  
  -- Could NOT find Doxygen (missing:  DOXYGEN_EXECUTABLE) 
  </code></pre>
  
  <p>What does this mean?</p>