treewide: prevent redefining names

gcc dislikes a member name that matches a type name, as it changes
the type name retroactively. Fix by fully-qualifying the type name,
so it is not changed by the newly-introduced member.

db/view/view.hh

@@ -111,7 +111,7 @@ public:
         return _row.is_live(s, column_kind(), base_tombstone, now);
     }
 
-    column_kind column_kind() const {
+    ::column_kind column_kind() const {
         return _key.has_value()
                 ? column_kind::regular_column : column_kind::static_column;
     }