Unbreak VC++ build.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9528cb4..1dcf9fda 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -29,6 +29,7 @@
 #include <iostream>
 #include <set>
 #include <algorithm>
+#include <cmath>
 using namespace llvm;
 
 /// makeVTList - Return an instance of the SDVTList struct initialized with the