Define equality of value_sett::object_mapt

This was removed recently in pull request diffblue#4694 but it
seems necessary when compiling with clang which would complain about it
not being defined.

Author: romainbrenguier

src/pointer-analysis/value_set.h

@@ -547,4 +547,10 @@ class value_sett
   }
 };
 
+bool operator==(
+  const value_sett::object_mapt &map1, const value_sett::object_mapt &map2)
+{
+  return map1.read() == map2.read();
+}
+
 #endif // CPROVER_POINTER_ANALYSIS_VALUE_SET_H