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/interest.hpp b/src/interest.hpp
index 121541b..52cabf7 100644
--- a/src/interest.hpp
+++ b/src/interest.hpp
@@ -338,6 +338,8 @@
   mutable Block m_wire;
 };
 
+NDN_CXX_DECLARE_WIRE_ENCODE_INSTANTIATIONS(Interest);
+
 std::ostream&
 operator<<(std::ostream& os, const Interest& interest);