The current warning in -Wnull-arithmetic for comparisons between NULL and...

The current warning in -Wnull-arithmetic for comparisons between NULL and non-pointers is not very helpful.  This patch will update the wording to be more helpful to users.

Old warning:

warning: use of NULL in arithmetic operation [-Wnull-arithmetic]
  return 10 <= NULL;
            ^  ~~~~

New warning:

warning: comparison between NULL and non-pointer ('int' and NULL) [-Wnull-arithmetic]
  return 10 <= NULL;
         ~~ ^  ~~~~
llvm-svn: 137377