Add a missing #include, patch courtesy of Baptiste Lepilleur.

llvm-svn: 23302
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index bffc176..ddbe45a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -40,6 +40,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Target/TargetLowering.h"
+#include <algorithm>
 #include <cmath>
 using namespace llvm;