libctf, link: add lazy linking: clean up input members: err/warn cleanup

This rather large and intertwined pile of changes does three things:

First, it transitions from dprintf to ctf_err_warn for things the user might
care about: this one file is the major impetus for the ctf_err_warn
infrastructure, because things like file names are crucial in linker
error messages, and errno values are utterly incapable of
communicating them

Second, it stabilizes the ctf_link APIs: you can now call
ctf_link_add_ctf without a CTF argument (only a NAME), to lazily
ctf_open the file with the given NAME when needed, and close it as soon
as possible, to save memory.  This is not an API change because a null
CTF argument was prohibited before now.

Since getting CTF directly from files uses ctf_open, passing in only a
NAME requires use of libctf, not libctf-nobfd.  The linker's behaviour
is unchanged, as it still passes in a ctf_archive_t as before.

This also let us fix a leak: we were opening ctf_archives and their
containing ctf_files, then only closing the files and leaving the
archives open.

Third, this commit restructures the ctf_link_in_member argument used by
the CTF linking machinery and adjusts its users accordingly.

We drop two members:

- arcname, which is difficult to construct and then only used in error
  messages (that were only dprintf()ed, so never seen!)
- share_mode, since we store the flags passed to ctf_link (including the
  share mode) in a new ctf_file_t.ctf_link_flags to help dedup get hold
  of it

We rename others whose existing names were fairly dreadful:

- done_main_member -> done_parent, using consistent terminology for .ctf
  as the parent of all archive members
- main_input_fp -> in_fp_parent, likewise
- file_name -> in_file_name, likewise

We add one new member, cu_mapped.

Finally, we move the various frees of things like mapping table data to
the top-level ctf_link, since deduplicating links will want to do that
too.

include/
	* ctf-api.h (ECTF_NEEDSBFD): New.
	(ECTF_NERR): Adjust.
	(ctf_link): Rename share_mode arg to flags.
libctf/
	* Makefile.am: Set -DNOBFD=1 in libctf-nobfd, and =0 elsewhere.
	* Makefile.in: Regenerated.
	* ctf-impl.h (ctf_link_input_name): New.
	(ctf_file_t) <ctf_link_flags>: New.
	* ctf-create.c (ctf_serialize): Adjust accordingly.
	* ctf-link.c: Define ctf_open as weak when PIC.
	(ctf_arc_close_thunk): Remove unnecessary thunk.
	(ctf_file_close_thunk): Likewise.
	(ctf_link_input_name): New.
	(ctf_link_input_t): New value of the ctf_file_t.ctf_link_input.
	(ctf_link_input_close): Adjust accordingly.
	(ctf_link_add_ctf_internal): New, split from...
	(ctf_link_add_ctf): ... here.  Return error if lazy loading of
	CTF is not possible.  Change to just call...
	(ctf_link_add): ... this new function.
	(ctf_link_add_cu_mapping): Transition to ctf_err_warn.  Drop the
	ctf_file_close_thunk.
	(ctf_link_in_member_cb_arg_t) <file_name> Rename to...
	<in_file_name>: ... this.
	<arcname>: Drop.
	<share_mode>: Likewise (migrated to ctf_link_flags).
	<done_main_member>: Rename to...
	<done_parent>: ... this.
	<main_input_fp>: Rename to...
	<in_fp_parent>: ... this.
	<cu_mapped>: New.
	(ctf_link_one_type): Adjuwt accordingly.  Transition to
	ctf_err_warn, removing a TODO.
	(ctf_link_one_variable): Note a case too common to warn about.
	Report in the debug stream if a cu-mapped link prevents addition
	of a conflicting variable.
	(ctf_link_one_input_archive_member): Adjust.
	(ctf_link_lazy_open): New, open a CTF archive for linking when
	needed.
	(ctf_link_close_one_input_archive): New, close it again.
	(ctf_link_one_input_archive): Adjust for lazy opening, member
	renames, and ctf_err_warn transition.  Move the
	empty_link_type_mapping call to...
	(ctf_link): ... here.  Adjut for renamings and thunk removal.
	Don't spuriously fail if some input contains no CTF data.
	(ctf_link_write): ctf_err_warn transition.
	* libctf.ver: Remove not-yet-stable comment.

libctf/ctf-create.c

@@ -542,6 +542,7 @@ ctf_serialize (ctf_file_t *fp)
   nfp->ctf_link_type_mapping = fp->ctf_link_type_mapping;
   nfp->ctf_link_memb_name_changer = fp->ctf_link_memb_name_changer;
   nfp->ctf_link_memb_name_changer_arg = fp->ctf_link_memb_name_changer_arg;
+  nfp->ctf_link_flags = fp->ctf_link_flags;
 
   nfp->ctf_snapshot_lu = fp->ctf_snapshots;