title: cmake check existence of compiler
body: <p>I'm trying to play around with <code>cmake</code> to build a small C++-code.</p>
  
  <p>I do not have yet <code>g++</code> 
  (I'm testing on a virtualbox OS)</p>
  
  <p>When I call <code>cmake .</code>
  I get the nasty error messages. </p>
  
  <pre><code>-- The C compiler identification is GNU 4.7.2
  
  **-- The CXX compiler identification is unknown**
  
  -- Check for working C compiler: /usr/bin/gcc
  
  -- Check for working C compiler: /usr/bin/gcc -- works
  
  -- Detecting C compiler ABI info
  
  -- Detecting C compiler ABI info - done
  
  **CMake Error: your CXX compiler: "CMAKE_CXX_COMPILER-NOTFOUND" was not found.   Please set CMAKE_CXX_COMPILER to a valid compiler path or name.
  
  -- Configuring incomplete, errors occurred!**
  </code></pre>
  
  <p>Basically, this is OK. It says errors occurred, but it says too much than needed. I just want to get a precise and concise message saying "g++ ist not installed. INSTALL it please".</p>
  
  <p>Is there a way to first check if <code>g++</code> is installed and then give an appropriate message? </p>