missing BOOST_FALLTHROUGH in a few cases

Author: Roy

include/boost/json/basic_parser_impl.hpp

@@ -686,10 +686,17 @@ parse_value(const char* p,
             // or just leave it as is
             if(BOOST_JSON_UNLIKELY(p == sentinel()))
                 return maybe_suspend(p, state::val2);
-            // intentional fallthrough
+            BOOST_FALLTHROUGH;
+
         case ' ':
+            BOOST_FALLTHROUGH;
+
         case '\t':
+            BOOST_FALLTHROUGH;
+
         case '\n':
+            BOOST_FALLTHROUGH;
+
         case '\r':
             p = detail::count_whitespace(p, end_);
             if(BOOST_JSON_UNLIKELY(p == end_))