add (lib)attr and libacl as optional libraries

when libacl is built and --enable-fpm is used, also enable --with-fpm-acl

src/SPC/builder/linux/library/attr.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SPC\builder\linux\library;
+
+class attr extends LinuxLibraryBase
+{
+    use \SPC\builder\unix\library\attr;
+
+    public const NAME = 'attr';
+}