libctf, binutils: dump the CTF header

The CTF header has before now been thrown away too soon to be dumped
using the ctf_dump() machinery used by objdump and readelf: instead, a
kludge involving debugging-priority dumps of the header offsets on every
open was used.

Replace this with proper first-class dumping machinery just like
everything else in the CTF file, and have objdump and readelf use it.
(The dumper already had an enum value in ctf_sect_names_t for this
purpose, waiting to be used.)

v5: fix tabdamage.

libctf/
	* ctf-impl.h (ctf_file_t): New field ctf_openflags.
	* ctf-open.c (ctf_bufopen): Set it.  No longer dump header offsets.
	* ctf-dump.c (dump_header): New function, dump the CTF header.
	(ctf_dump): Call it.
	(ctf_dump_header_strfield): New function.
	(ctf_dump_header_sectfield): Likewise.

binutils/
	* objdump.c (dump_ctf_archive_member): Dump the CTF header.
	* readelf.c (dump_section_as_ctf): Likewise.