This means that any archive containing dicts can get its strings dedupped
together, rather than only those that are ctf_linked.
(For now, we are still constrained to ctf_linked archives, since fixing that
requires further changes to ctf_dedup_strings: but this gives us the first
half of what is necessary.)
libctf/
* ctf-link.c (ctf_link_write): Move string dedup into...
* ctf-archive.c (ctf_arc_preserialize): ... this new function.
(ctf_arc_write_fd): Call it.
This file is a bit of a grab-bag of dict-wide API functions like
ctf_set_open_errno or ctf_errwarning_next and portabilty functions and
wrappers like ctf_mmap or ctf_pread.
Split the latter out, and move other dict-wide functions that got
stuck in ctf-util.c (because it was so hard to tell the two files
apart) into ctf-api.c where they belong.
