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/StrongPHIElimination.cpp b/lib/CodeGen/StrongPHIElimination.cpp
index 227eb47..0fabd8e 100644
--- a/lib/CodeGen/StrongPHIElimination.cpp
+++ b/lib/CodeGen/StrongPHIElimination.cpp
@@ -47,6 +47,7 @@
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Debug.h"
 using namespace llvm;