qsort: ldctor.c CONSTRUCTORS

qsort: ldctor.c CONSTRUCTORS

ctor_cmp had an ineffective comparison of addresses in an attempt to
ensure sort stability.  Comparing the addresses passed to the
comparison function can't work since those addresses may be from an
array that is already perturbed by qsort.

	* ldctor.h (struct set_element): Make next field a union, adding
	idx field.
	* ldctor.c (ctor_cmp): Dereference pointer and lose unnecessary
	const.  Replace final sort on pointer value with final sort on idx.
	(ldctor_add_set_entry): Adjust next field access.
	(ldctor_build_sets): Likewise.  Set u.idx field for sort.