libctf, link: fix spurious conflicts of variables in the variable section

libctf, link: fix spurious conflicts of variables in the variable section

When we link a CTF variable, we check to see if it already exists in the
parent dict first: if it does, and it has a type the same as the type we
would populate it with, we assume we don't need to do anything:
otherwise, we populate it in a per-CU child.

Or that's what we should be doing.  Instead, we check if the type is the
same as the type in *source dict*, which is going to be a completely
different value!  So we end up concluding all variables are conflicting,
bloating up output possibly quite a lot (variables aren't big in and of
themselves, but each drags around a strtab entry, and CTF dicts in a CTF
archive do not share their strtabs -- one of many problems with CTF
archives as presently constituted.)

Fix trivial: check the right type.

libctf/
	* ctf-link.c (ctf_link_one_variable): Check the dst_type for
	conflicts, not the source type.