Enable a seconary allocator support (e.g. GWP-Asan) (#737)

src/test/perf/external_pointer/externalpointer.cc

@@ -76,12 +76,16 @@ namespace test
         size_t rand = (size_t)r.next();
         size_t oid = rand & (((size_t)1 << count_log) - 1);
         size_t* external_ptr = objects[oid];
+        if (!alloc.is_snmalloc_owned(external_ptr))
+          continue;
         size_t size = *external_ptr;
         size_t offset = (size >> 4) * (rand & 15);
         void* interior_ptr = pointer_offset(external_ptr, offset);
         void* calced_external = alloc.external_pointer(interior_ptr);
         if (calced_external != external_ptr)
+        {
           abort();
+        }
       }
     }