[PATCH] Header guard warning is too agressive

[Ted Kremenek]

  This warning is turning out to be quite noisy.  The edit distance heuristic, while not a complete fix for PR17053, would potentially help make this warning more useful in practice regardless.

  For example, I'm seeing a warning on the following code:

    #ifndef NO_SYSCALL_LEGACY

    #define _NONSTD_SOURCE`

  The edit distance heuristic would not warn here.  Even if the edit distance heuristic doesn't solve the complete problem, it would be good to make some incremental progress here.

http://llvm-reviews.chandlerc.com/D1506