serialization: declare do_serialize specializations before use

This lets my gcc picks those instead of the generic template
where appropriate (and then fail since std::vector<something>
does not have a serialize method.

src/serialization/vector.h

@@ -32,6 +32,11 @@
 
 #include "serialization.h"
 
+template <template <bool> class Archive, class T>
+bool do_serialize(Archive<false> &ar, std::vector<T> &v);
+template <template <bool> class Archive, class T>
+bool do_serialize(Archive<true> &ar, std::vector<T> &v);
+
 namespace serialization
 {
   namespace detail