Add -Wextra-semi -Wundefined-func-template to the default CXXFLAGS

And fix the resulting compilation errors.

Change-Id: I16f679836a0cf2a3ff5dfcf6f6b67bfbfe4cdbd7
Refs: #4248
diff --git a/src/lp/cache-policy.hpp b/src/lp/cache-policy.hpp
index 45b9493..f35dc06 100644
--- a/src/lp/cache-policy.hpp
+++ b/src/lp/cache-policy.hpp
@@ -103,6 +103,8 @@
   mutable Block m_wire;
 };
 
+NDN_CXX_DECLARE_WIRE_ENCODE_INSTANTIATIONS(CachePolicy);
+
 } // namespace lp
 } // namespace ndn