Add set_consume which always takes ownership

Freeing in error path is the common pattern with set_put().

src/shared/install.c

@@ -178,11 +178,9 @@ static int mark_symlink_for_removal(
 
         path_kill_slashes(n);
 
-        r = set_put(*remove_symlinks_to, n);
-        if (r < 0) {
-                free(n);
+        r = set_consume(*remove_symlinks_to, n);
+        if (r < 0)
                 return r == -EEXIST ? 0 : r;
-        }
 
         return 0;
 }

src/shared/set.c

@@ -49,6 +49,13 @@ int set_put(Set *s, void *value) {
         return hashmap_put(MAKE_HASHMAP(s), value, value);
 }
 
+int set_consume(Set *s, void *value) {
+        int r = set_put(s, value);
+        if (r < 0)
+                free(value);
+        return r;
+}
+
 int set_replace(Set *s, void *value) {
         return hashmap_replace(MAKE_HASHMAP(s), value, value);
 }

src/shared/set.h

@@ -46,6 +46,7 @@ Set* set_copy(Set *s);
 int set_ensure_allocated(Set **s, hash_func_t hash_func, compare_func_t compare_func);
 
 int set_put(Set *s, void *value);
+int set_consume(Set *s, void *value);
 int set_replace(Set *s, void *value);
 void *set_get(Set *s, void *value);
 bool set_contains(Set *s, void *value);