0.8.4.3

0.8.4.3
	Inline arch_os_get_current_thread.  This means putting it in
	thread.h, which may be considered a little silly.  When >1
	arch/os combination supports threading, maybe we need a
	late-target-arch-os.h file or similar.  In the meantime I'm
	not going to turn the build upside down right now.