I forgot to note this the last publically-visible struct which may be
packed.  Internals for the others are defined privately:

	$ pahole -P ruby
	rb_thread_struct	1016	1000	16
	rb_execarg	160	152	8
	io_internal_writev_struct	24	16	8
	io_advise_struct	32	24	8
	waitpid_arg	24	16	8
	load_file_arg	48	40	8
	rb_econv_t	200	184	16
	rb_transcoder	160	152	8
	rb_context_struct	1312	1304	8
	rb_fiber_struct	2304	2296	8
	parser_params	320	304	16