Add packing to class Thread.

Otherwise, code compiled on the host can use different offsets than
we need for the same structure on the target.

Also add commented-out code to start up the various GC daemon threads.
More Class native methods need to be implemented before that will work.

Change-Id: I618b647b92378eec1b25cee469c8cfccf42f21fd
diff --git a/src/object.h b/src/object.h
index 02c98d8..8addcc6 100644
--- a/src/object.h
+++ b/src/object.h
@@ -185,7 +185,7 @@
 
 // Classes shared with the managed side of the world need to be packed
 // so that they don't have extra platform specific padding.
-#define MANAGED __attribute__ ((__packed__))
+#define MANAGED PACKED
 
 // C++ mirror of java.lang.Object
 class MANAGED Object {