title: What is GCC_NO_COMMON_BLOCKS used for?
body: <p>I found that my project sets </p>
  
  <pre><code>GCC_NO_COMMON_BLOCKS = NO 
  </code></pre>
  
  <p>under Apple LLVM Compiler 3.1 - Code Generation settings, as "No Common Blocks"</p>
  
  <p><img src="https://i.stack.imgur.com/vU3Ma.png" alt="enter image description here"></p>
  
  <p>I would like to know: <strong>what is that flag used for?</strong></p>
  
  <p>Thanks a lot</p>