Update vm->self location and mark it in vm.c for consistency

Author: tagomoris

gc.c

@@ -3060,7 +3060,6 @@ rb_gc_mark_roots(void *objspace, const char **categoryp)
 
     MARK_CHECKPOINT("vm");
     rb_vm_mark(vm);
-    if (vm->self) gc_mark_internal(vm->self);
 
     MARK_CHECKPOINT("end_proc");
     rb_mark_end_proc();

vm.c

@@ -2982,6 +2982,7 @@ rb_vm_update_references(void *ptr)
     if (ptr) {
         rb_vm_t *vm = ptr;
 
+        vm->self = rb_gc_location(vm->self);
         vm->mark_object_ary = rb_gc_location(vm->mark_object_ary);
         vm->load_path = rb_gc_location(vm->load_path);
         vm->load_path_snapshot = rb_gc_location(vm->load_path_snapshot);
@@ -3068,6 +3069,8 @@ rb_vm_mark(void *ptr)
             rb_gc_mark_maybe(*list->varptr);
         }
 
+        rb_gc_mark_movable(vm->self);
+
         if (vm->main_namespace) {
             rb_namespace_entry_mark((void *)vm->main_namespace);
         }