Add ISC_LIST_FOREACH(_SAFE) macros

There's a recurring pattern walking the ISC_LISTs that just repeats over
and over.  Add two macros:

 * ISC_LIST_FOREACH(list, elt, link) - walk the static list
 * ISC_LIST_FOREACH_SAFE(list, elt, link, next) - walk the list in
   a manner that's safe against list member deletions

Author: oerdnj

.clang-format

@@ -78,4 +78,4 @@ PenaltyBreakString: 80
 PenaltyExcessCharacter: 100
 Standard: Cpp11
 ContinuationIndentWidth: 8
-ForEachMacros: [ 'cds_lfs_for_each', 'cds_lfs_for_each_safe', 'cds_list_for_each_entry_safe' ]
+ForEachMacros: [ 'cds_lfs_for_each', 'cds_lfs_for_each_safe', 'cds_list_for_each_entry_safe', 'ISC_LIST_FOREACH', 'ISC_LIST_FOREACH_SAFE' ]

lib/isc/include/isc/list.h

@@ -227,3 +227,17 @@
 		INSIST(ISC_LIST_EMPTY(dest));   \
 		ISC_LIST_MOVEUNSAFE(dest, src); \
 	}
+
+/* clang-format off */
+#define ISC_LIST_FOREACH(list, elt, link)	\
+	for (elt = ISC_LIST_HEAD(list);		\
+	     elt != NULL;			\
+	     elt = ISC_LIST_NEXT(elt, link))
+/* clang-format on */
+
+/* clang-format off */
+#define ISC_LIST_FOREACH_SAFE(list, elt, link, next)						\
+	for (elt = ISC_LIST_HEAD(list), next = (elt != NULL) ? ISC_LIST_NEXT(elt, link) : NULL;	\
+	     elt != NULL;									\
+	     elt = next, next = (elt != NULL) ? ISC_LIST_NEXT(elt, link) : NULL)
+/* clang-format on */