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/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 10a3565..9248662 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -33,6 +33,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/STLExtras.h"
 #include <algorithm>
+#include <cmath>
 using namespace llvm;
 
 namespace {