title: gcov warning: merge mismatch for summaries
body: <p>Can anyone tell me what the gcov message "Merge mismatch for summaries" means? I have found the message in the gcc source here:</p>
  
  <p><a href="http://www.opensource.apple.com/source/gcc/gcc-5646/gcc/libgcov.c" rel="noreferrer">http://www.opensource.apple.com/source/gcc/gcc-5646/gcc/libgcov.c</a></p>
  
  <p>It seems to be a sanity check that the tags in the <code>.gcda</code> files match, but I'm not sure.  Anyone know how to work around this?</p>