Update Clang for 3.5 rebase (r209713).

Change-Id: I8c9133b0f8f776dc915f270b60f94962e771bc83
diff --git a/lib/Analysis/FormatString.cpp b/lib/Analysis/FormatString.cpp
index 43ecc66..851b97e 100644
--- a/lib/Analysis/FormatString.cpp
+++ b/lib/Analysis/FormatString.cpp
@@ -507,7 +507,7 @@
   case None:
     return "";
   }
-  return NULL;
+  return nullptr;
 }
 
 //===----------------------------------------------------------------------===//
@@ -539,7 +539,7 @@
   case nArg: return "n";
   case PercentArg:  return "%";
   case ScanListArg: return "[";
-  case InvalidSpecifier: return NULL;
+  case InvalidSpecifier: return nullptr;
 
   // POSIX unicode extensions.
   case CArg: return "C";
@@ -551,7 +551,7 @@
   // GlibC specific specifiers.
   case PrintErrno: return "m";
   }
-  return NULL;
+  return nullptr;
 }
 
 Optional<ConversionSpecifier>