Fix macOS build after enabling Generational CC by default in ART.

Address link-time failures when building libartd on macOS after
turning on Generational CC collection by default in ART.

Test: mmma art (on macOS and Linux)
Bug: 67628039
Change-Id: Id464459a8ce0d7276755750cf4c10feb54009704
diff --git a/runtime/scoped_thread_state_change.cc b/runtime/scoped_thread_state_change.cc
index edbce05..ae833b4 100644
--- a/runtime/scoped_thread_state_change.cc
+++ b/runtime/scoped_thread_state_change.cc
@@ -20,6 +20,7 @@
 
 #include "base/casts.h"
 #include "jni/java_vm_ext.h"
+#include "mirror/object-inl.h"
 #include "obj_ptr-inl.h"
 #include "runtime-inl.h"