xo-alloc, xo-object: fix alloc,gc unit tests after gc improvements

src/alloc/GC.cpp

@@ -233,6 +233,12 @@ namespace xo {
             return nursery_to()->page_size();
         }
 
+        std::size_t
+        GC::hugepage_z() const
+        {
+            return nursery_to()->hugepage_z();
+        }
+
         std::size_t
         GC::nursery_from_allocated() const
         {