be explicit about types

Author: RalfJung

src/eval.rs

@@ -132,9 +132,9 @@ impl Default for MiriConfig {
             forwarded_env_vars: vec![],
             args: vec![],
             seed: None,
-            tracked_pointer_tags: Default::default(),
-            tracked_call_ids: Default::default(),
-            tracked_alloc_ids: Default::default(),
+            tracked_pointer_tags: HashSet::default(),
+            tracked_call_ids: HashSet::default(),
+            tracked_alloc_ids: HashSet::default(),
             tag_raw: false,
             data_race_detector: true,
             cmpxchg_weak_failure_rate: 0.8,