Add identity for std::mutex

library/include/DataIdentity.h

@@ -25,10 +25,11 @@ distribution.
 #pragma once
 
 #include <deque>
-#include <string>
+#include <map>
+#include <mutex>
 #include <sstream>
+#include <string>
 #include <vector>
-#include <map>
 
 #include "DataDefs.h"
 
@@ -570,6 +571,11 @@ namespace df
         static opaque_identity *get() { return &identity; }
     };
 
+    template<> struct DFHACK_EXPORT identity_traits<std::mutex> {
+        static opaque_identity identity;
+        static opaque_identity *get() { return &identity; }
+    };
+
     template<> struct DFHACK_EXPORT identity_traits<char*> {
         static ptr_string_identity identity;
         static ptr_string_identity *get() { return &identity; }