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/signature-info.cpp b/src/signature-info.cpp
index 1fc68f9..36964ac 100644
--- a/src/signature-info.cpp
+++ b/src/signature-info.cpp
@@ -82,11 +82,7 @@
   return totalLength;
 }
 
-template size_t
-SignatureInfo::wireEncode<encoding::EncoderTag>(EncodingImpl<encoding::EncoderTag>& encoder) const;
-
-template size_t
-SignatureInfo::wireEncode<encoding::EstimatorTag>(EncodingImpl<encoding::EstimatorTag>& encoder) const;
+NDN_CXX_DEFINE_WIRE_ENCODE_INSTANTIATIONS(SignatureInfo);
 
 const Block&
 SignatureInfo::wireEncode() const