[C++11] Make use of 'nullptr' in the Support library.

llvm-svn: 205697
diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index 5472e0e..38f3ec7 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -47,7 +47,7 @@
              void *DiagHandlerCtxt)
   : IO(Ctxt),
     Strm(new Stream(InputContent, SrcMgr)),
-    CurrentNode(NULL) {
+    CurrentNode(nullptr) {
   if (DiagHandler)
     SrcMgr.setDiagHandler(DiagHandler, DiagHandlerCtxt);
   DocIterator = Strm->begin();
@@ -351,7 +351,7 @@
     return new EmptyHNode(N);
   } else {
     setError(N, "unknown node kind");
-    return NULL;
+    return nullptr;
   }
 }