Unbreak VC++ build.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp b/lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp
index 1b8f399..161873c 100644
--- a/lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp
+++ b/lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Target/TargetData.h"
 #include <csignal>
 #include <map>
+#include <cmath>
 using std::vector;
 
 using namespace llvm;