libctf, dedup: add deduplicator

This adds the core deduplicator that the ctf_link machinery calls
(possibly repeatedly) to link the CTF sections: it takes an array
of input ctf_file_t's and another array that indicates which entries in
the input array are parents of which other entries, and returns an array
of outputs.  The first output is always the ctf_file_t on which
ctf_link/ctf_dedup/etc was called: the other outputs are child dicts
that have the first output as their parent.

include/
	* ctf-api.h (CTF_LINK_SHARE_DUPLICATED): No longer unimplemented.
libctf/
	* ctf-impl.h (ctf_type_id_key): New, the key in the
	cd_id_to_file_t.
	(ctf_dedup): New, core deduplicator state.
	(ctf_file_t) <ctf_dedup>: New.
	<ctf_dedup_atoms>: New.
	<ctf_dedup_atoms_alloc>: New.
	(ctf_hash_type_id_key): New prototype.
	(ctf_hash_eq_type_id_key): Likewise.
	(ctf_dedup_atoms_init): Likewise.
	* ctf-hash.c (ctf_hash_eq_type_id_key): New.
	(ctf_dedup_atoms_init): Likewise.
	* ctf-create.c (ctf_serialize): Adjusted.
	(ctf_add_encoded): No longer static.
	(ctf_add_reftype): Likewise.
	* ctf-open.c (ctf_file_close): Destroy the
	ctf_dedup_atoms_alloc.
	* ctf-dedup.c: New file.
        * ctf-decls.h [!HAVE_DECL_STPCPY]: Add prototype.
	* configure.ac: Check for stpcpy.
	* Makefile.am: Add it.
	* Makefile.in: Regenerate.
        * config.h.in: Regenerate.
        * configure: Regenerate.

libctf/ctf-decls.h

@@ -72,4 +72,8 @@ void ctf_qsort_r (void *base, size_t nmemb, size_t size,
 #define MAX(a, b) ((a) > (b) ? (a) : (b))
 #define MIN(a, b) ((a) < (b) ? (a) : (b))
 
+#if !HAVE_DECL_STPCPY
+extern char *stpcpy (char *, const char *);
+#endif
+
 #endif /* _CTF_DECLS_H */