xo-gc: missed files in prev commit

include/xo/gc/setup_gc.hpp

@@ -0,0 +1,20 @@
+/** @file SetupGc.hpp
+ *
+ *  @author Roland Conybeare, Mar 2026
+ **/
+
+#pragma once
+
+namespace xo {
+    namespace mm {
+
+        class SetupGc {
+        public:
+            /** Register gc (facet,impl) combinations with FacetRegistry **/
+            static bool register_facets();
+        };
+
+    } /*namespace mm*/
+} /*namespace xo*/
+
+/* end SetupGc.hpp */