Merge branch '3306-undefined-macros-in-contrib-dlz-modules-wildcard-dlz_wildcard_dynamic-c' into 'main'

Resolve "Undefined macros in contrib/dlz/modules/wildcard/dlz_wildcard_dynamic.c"

Closes #3306

See merge request isc-projects/bind9!6203

CHANGES

@@ -1,3 +1,5 @@
+5879.	[contrib]	dlz: Add FALLTHROUGH and UNREACHABLE macros. [GL #3306]
+
 5878.	[func]		Check the algorithm name or OID embedded at the start
 			of the signature field for PRIVATEDNS and PRIVATEOID
 			SIG and RRSIG records are well formed. [GL #3296]

contrib/dlz/modules/include/dlz_minimal.h

@@ -27,6 +27,7 @@
 
 #include <inttypes.h>
 #include <stdbool.h>
+#include <stdlib.h>
 
 #include <arpa/inet.h>
 #include <net/if.h>
@@ -85,6 +86,24 @@ typedef uint32_t     dns_ttl_t;
 		var = _u.v;            \
 	} while (0)
 
+#if !defined(__has_attribute)
+#define __has_attribute(x) 0
+#endif /* if !defined(__has_attribute) */
+
+#if __GNUC__ >= 7 || __has_attribute(fallthrough)
+#define FALLTHROUGH __attribute__((fallthrough))
+#else
+/* clang-format off */
+#define FALLTHROUGH do {} while (0) /* FALLTHROUGH */
+/* clang-format on */
+#endif
+
+#ifdef __GNUC__
+#define UNREACHABLE() __builtin_unreachable()
+#else
+#define UNREACHABLE() abort()
+#endif
+
 /* opaque structures */
 typedef void *dns_sdlzlookup_t;
 typedef void *dns_sdlzallnodes_t;