Unbreak VC++ build.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 1b355b6..359766d 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -20,6 +20,7 @@
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
 #include <cerrno>
+#include <cmath>
 using namespace llvm;
 
 //===----------------------------------------------------------------------===//