Trim an unneeded header.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137184 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp
index 6b801cb..3a6211a 100644
--- a/lib/CodeGen/TailDuplication.cpp
+++ b/lib/CodeGen/TailDuplication.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/Statistic.h"