libctf: make ctf_bfdopen_ctfsect a debugger entry point

libctf: make ctf_bfdopen_ctfsect a debugger entry point

This makes it possible to use LIBCTF_DEBUG to debug things that happen
before the ctf_bfdopen_internal call that ctf_bfdopen_ctfsect eventually
thunks down to (symtab/strtab lookup, archive opening, etc).

This is not important for ctf_open callers, since ctf_fdopen already
calls libctf_init_debug, but ctf_bfdopen_ctfsect is a public entry point
that can be called directly (e.g. objdump and readelf both do so).

libctf/ChangeLog
2021-03-25  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-open-bfd.c (ctf_bfdopen_ctfsect): Initialize debugging.