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

And fix the resulting compilation errors.

Change-Id: I2f8a8406542d297bfeeb4c922812ff1879a4dff6
Refs: #4248
diff --git a/tools/ndn-autoconfig/main.cpp b/tools/ndn-autoconfig/main.cpp
index fad4933..b7340a3 100644
--- a/tools/ndn-autoconfig/main.cpp
+++ b/tools/ndn-autoconfig/main.cpp
@@ -38,6 +38,11 @@
 #include <ndn-cxx/util/scheduler-scoped-event-id.hpp>
 #include <ndn-cxx/util/time.hpp>
 
+// suppress warning caused by boost::program_options::parse_config_file
+#ifdef __clang__
+#pragma clang diagnostic ignored "-Wundefined-func-template"
+#endif
+
 namespace ndn {
 namespace tools {
 namespace autoconfig {