systemctl: enable: overwrite broken alias symlinks

When switching to an alternative alias provider,
the previous one might have been uninstalled or so.
It should be fine for us to overwrite them directly.

Closes #23694

src/shared/install.c

@@ -1892,6 +1892,7 @@ static int install_info_symlink_alias(
 
         STRV_FOREACH(s, info->aliases) {
                 _cleanup_free_ char *alias_path = NULL, *dst = NULL, *dst_updated = NULL;
+                bool broken;
 
                 q = install_name_printf(scope, info, *s, &dst);
                 if (q < 0) {
@@ -1912,7 +1913,14 @@ static int install_info_symlink_alias(
                 if (!alias_path)
                         return -ENOMEM;
 
-                q = create_symlink(lp, info->path, alias_path, force, changes, n_changes);
+                q = chase_symlinks(alias_path, lp->root_dir, CHASE_NONEXISTENT, NULL, NULL);
+                if (q < 0 && q != -ENOENT) {
+                        r = r < 0 ? r : q;
+                        continue;
+                }
+                broken = q == 0; /* symlink target does not exist? */
+
+                q = create_symlink(lp, info->path, alias_path, force || broken, changes, n_changes);
                 r = r < 0 ? r : q;
         }