* sbitmap.c (sbitmap_verify_popcount, sbitmap_alloc_with_popcount,
	sbitmap_copy, sbitmap_copy_n, sbitmap_equal, sbitmap_empty_p,
	sbitmap_union_of_diff_cg, sbitmap_union_of_diff, sbitmap_not,
	sbitmap_difference, sbitmap_any_common_bits, sbitmap_a_and_b_cg,
	sbitmap_a_and_b, sbitmap_a_xor_b_cg, sbitmap_a_xor_b,
	sbitmap_a_or_b_cg, sbitmap_a_or_b, sbitmap_a_subset_b_p,
	sbitmap_a_or_b_and_c_cg, sbitmap_a_or_b_and_c,
	sbitmap_a_and_b_or_c_cg, sbitmap_a_and_b_or_c,
	sbitmap_first_set_bit, sbitmap_last_set_bit, dump_sbitmap,
	dump_sbitmap_file, debug_sbitmap, popcount_table,
	sbitmap_popcount): Constify.
	* sbitmap.h (const_sbitmap, const_sbitmap_ptr): New.
	(sbitmap_iterator, sbitmap_iter_init, dump_sbitmap,
	dump_sbitmap_file, sbitmap_copy, sbitmap_copy_n, sbitmap_equal,
	sbitmap_empty_p, sbitmap_union_of_diff, sbitmap_union_of_diff_cg,
	sbitmap_difference, sbitmap_not, sbitmap_a_or_b_and_c,
	sbitmap_a_or_b_and_c_cg, sbitmap_a_and_b_or_c,
	sbitmap_a_and_b_or_c_cg, sbitmap_any_common_bits, sbitmap_a_and_b,
	sbitmap_a_and_b_cg, sbitmap_a_or_b, sbitmap_a_or_b_cg,
	sbitmap_a_xor_b, sbitmap_a_xor_b_cg, sbitmap_a_subset_b_p,
	sbitmap_first_set_bit, sbitmap_last_set_bit, debug_sbitmap,
	sbitmap_popcount, sbitmap_verify_popcount): Constify.

From-SVN: r126929