Fix some memory leaks

src/gc.c

@@ -307,3 +307,26 @@ void lisp_gc_now(struct timespec *restrict time_took) {
     ++total_gc_count;
     lisp_doing_gc = false;
 }
+
+void lisp_gc_teardown(void) {
+    assert(the_stack.depth == 0);
+    while (white_objects) {
+        free_object(white_objects->obj);
+    }
+    while (grey_objects) {
+        free_object(grey_objects->obj);
+    }
+    while (black_objects) {
+        free_object(black_objects->obj);
+    }
+    while (static_objects) {
+        struct GCObjectList *next = static_objects->next;
+        free(static_objects);
+        static_objects = next;
+    }
+    while (free_objects_list) {
+        struct GCObjectList *next = free_objects_list->next;
+        free(free_objects_list);
+        free_objects_list = next;
+    }
+}