Add missing include file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349363 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Demangle/MicrosoftDemangleNodes.cpp b/lib/Demangle/MicrosoftDemangleNodes.cpp
index 930c838..a588dca 100644
--- a/lib/Demangle/MicrosoftDemangleNodes.cpp
+++ b/lib/Demangle/MicrosoftDemangleNodes.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Demangle/Compiler.h"
 #include "llvm/Demangle/Utility.h"
 #include <cctype>
+#include <string>
 
 using namespace llvm;
 using namespace ms_demangle;