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/data.hpp b/src/data.hpp
index eedea7a..2729e0d 100644
--- a/src/data.hpp
+++ b/src/data.hpp
@@ -241,6 +241,14 @@
   mutable Name m_fullName; ///< cached FullName computed from m_wire
 };
 
+#ifndef DOXYGEN
+extern template size_t
+Data::wireEncode<encoding::EncoderTag>(EncodingBuffer&, bool) const;
+
+extern template size_t
+Data::wireEncode<encoding::EstimatorTag>(EncodingEstimator&, bool) const;
+#endif
+
 std::ostream&
 operator<<(std::ostream& os, const Data& data);