fix formatting

Author: frasercrmck

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -18,8 +18,8 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"