Include <stddef.h>, for offsetof.

Include <stddef.h>, for offsetof.

(abitset_bytes): Return a size that is aligned
properly for vectors of objects.  Do not assume that adding a
header size to a multiple of a word size yields a value that is
properly aligned for the whole union.

(abitset_ones, abitset_zero, abitset_empty_p, abitset_copy1,
abitset_not, abitset_equal_p, abitset_subset_p, abitset_disjoint_p,
abitset_and, abitset_and_cmp, abitset_andn, abitset_andn_cmp,
abitset_or, abitset_or_cmp, abitset_xor, abitset_xor_cmp,
abitset_and_or, abitset_and_or_cmp, abitset_andn_or,
abitset_andn_or_cmp, abitset_or_and, abitset_or_and_cmp,
abitset_copy): Supply prototype decls, to improve the type-checking
that GCC can do.

(struct abitset_struct, abitset, struct bitset_struct): Remove.