net+util: fix build with gcc-7
Introduce an NDN_CXX_FALLTHROUGH macro to simplify
annotating switch cases that fall through.
Update code-style to recommend using NDN_CXX_FALLTHROUGH.
Change-Id: I80e4ff8d16a09f6ec9343f0480bc57ae0fcd1be4
diff --git a/src/util/backports-optional.hpp b/src/util/backports-optional.hpp
index 29862b1..8f1f498 100644
--- a/src/util/backports-optional.hpp
+++ b/src/util/backports-optional.hpp
@@ -42,17 +42,15 @@
#ifndef NDN_UTIL_BACKPORTS_OPTIONAL_HPP
#define NDN_UTIL_BACKPORTS_OPTIONAL_HPP
-#include "../common.hpp"
+#include "backports.hpp"
-#ifdef __has_include
-# if (__cplusplus > 201402L) && __has_include(<optional>)
-# include <optional>
-# define NDN_CXX_HAVE_STD_OPTIONAL
-# elif (__cplusplus > 201103L) && __has_include(<experimental/optional>)
-# include <experimental/optional>
-# if __cpp_lib_experimental_optional >= 201411
-# define NDN_CXX_HAVE_EXPERIMENTAL_OPTIONAL
-# endif
+#if (__cplusplus > 201402L) && NDN_CXX_HAS_INCLUDE(<optional>)
+# include <optional>
+# define NDN_CXX_HAVE_STD_OPTIONAL
+#elif (__cplusplus > 201103L) && NDN_CXX_HAS_INCLUDE(<experimental/optional>)
+# include <experimental/optional>
+# if __cpp_lib_experimental_optional >= 201411
+# define NDN_CXX_HAVE_EXPERIMENTAL_OPTIONAL
# endif
#endif