ART: Fix PACKED size of tls_ptr_size.

This should be PACKED to the current pointer size.

Change-Id: I31e23cd7f1fe57655b71b901642617df96a48aa1
diff --git a/runtime/thread.h b/runtime/thread.h
index 138c143..0d903db 100644
--- a/runtime/thread.h
+++ b/runtime/thread.h
@@ -1222,7 +1222,7 @@
     RuntimeStats stats;
   } tls64_;
 
-  struct PACKED(4) tls_ptr_sized_values {
+  struct PACKED(sizeof(void*)) tls_ptr_sized_values {
       tls_ptr_sized_values() : card_table(nullptr), exception(nullptr), stack_end(nullptr),
       managed_stack(), suspend_trigger(nullptr), jni_env(nullptr), tmp_jni_env(nullptr),
       self(nullptr), opeer(nullptr), jpeer(nullptr), stack_begin(nullptr), stack_size(0),