libctf: fix some tabdamage and move some code around

ctf-link.c is unnecessarily confusing because ctf_link_lazy_open is
positioned near functions that have nothing to do with opening files.

Move it around, and fix some tabdamage that's crept in lately.

libctf/ChangeLog
2021-03-18  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-link.c (ctf_link_lazy_open): Move up in the file, to near
	ctf_link_add_ctf.
	* ctf-lookup.c (ctf_lookup_symbol_idx): Repair tabdamage.
	(ctf_lookup_by_sym_or_name): Likewise.
	* testsuite/libctf-lookup/struct-iteration.c: Likewise.
	* testsuite/libctf-regression/type-add-unnamed-struct.c: Likewise.