[C++] Use 'nullptr'.

llvm-svn: 207083
diff --git a/llvm/lib/ExecutionEngine/MCJIT/SectionMemoryManager.cpp b/llvm/lib/ExecutionEngine/MCJIT/SectionMemoryManager.cpp
index f1dd5a6..9ceaa90 100644
--- a/llvm/lib/ExecutionEngine/MCJIT/SectionMemoryManager.cpp
+++ b/llvm/lib/ExecutionEngine/MCJIT/SectionMemoryManager.cpp
@@ -79,7 +79,7 @@
                                                           ec);
   if (ec) {
     // FIXME: Add error propagation to the interface.
-    return NULL;
+    return nullptr;
   }
 
   // Save this address as the basis for our next request