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.cpp b/src/interest.cpp
index 26b564e..60e284b 100644
--- a/src/interest.cpp
+++ b/src/interest.cpp
@@ -97,11 +97,7 @@
   return totalLength;
 }
 
-template size_t
-Interest::wireEncode<encoding::EncoderTag>(EncodingImpl<encoding::EncoderTag>& encoder) const;
-
-template size_t
-Interest::wireEncode<encoding::EstimatorTag>(EncodingImpl<encoding::EstimatorTag>& encoder) const;
+NDN_CXX_DEFINE_WIRE_ENCODE_INSTANTIATIONS(Interest);
 
 const Block&
 Interest::wireEncode() const