libctf: pass the thunk down properly when wrapping qsort_r

libctf: pass the thunk down properly when wrapping qsort_r

When wrapping qsort_r on a system like FreeBSD on which the compar
argument comes first, we wrap the passed arg in a thunk so we can pass
down both the caller-supplied comparator function and its argument.  We
should pass the *argument* down to the comparator, not the thunk, which
is basically random nonsense on the stack from the point of view of the
caller of qsort_r.

libctf/
	ctf-decls.h (ctf_qsort_compar_thunk): Fix arg passing.