libctf: types: unify code dealing with small-vs-large struct members

libctf: types: unify code dealing with small-vs-large struct members

This completes the job of unifying what was once three separate code
paths full of duplication for every function dealing with querying the
properties of struct and union members.  The dynamic code path was
already removed: this change removes the distinction between small and
large members, by adding a helper that copies out members from the vlen,
expanding small members into large ones as it does so.

This makes it possible to have *more* representations of things like
structure members without needing to change the querying functions at
all.  It also lets us check for buffer overruns more effectively,
verifying that we don't accidentally overrun the end of the vlen in
either the dynamic or static type case.

libctf/ChangeLog
2021-03-18  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-impl.h (ctf_next_t) <ctn_tp>: New.
	<u.ctn_mp>: Remove.
	<u.ctn_lmp>: Remove.
	<u.ctn_vlen>: New.
	* ctf-types.c (ctf_struct_member): New.
	(ctf_member_next): Use it, dropping separate large/small code paths.
	(ctf_type_align): Likewise.
	(ctf_member_info): Likewise.
	(ctf_type_rvisit): Likewise.