offset_int and widest_int are supposed to be at least one bit wider
than all the values they need to represent, with the extra bits
being signs.  Thus offset_int is effectively int128_t and widest_int
is effectively intNNN_t, for target-dependent NNN.

Because the types are signed, there's not really any need to specify
a sign for operations like comparison.  I think things would be clearer
if we supported <, <=, > and >= for them (but not for wide_int, which
doesn't have a sign).

Tested on x86_64-linux-gnu and aarch64-linux-gnu.

gcc/
	* wide-int.h: Update offset_int and widest_int documentation.
	(WI_SIGNED_BINARY_PREDICATE_RESULT): New macro.
	(wi::binary_traits): Allow ordered comparisons between offset_int and
	offset_int, between widest_int and widest_int, and between either
	of these types and basic C types.
	(operator <, <=, >, >=): Define for the same combinations.
	* tree.h (tree_int_cst_lt): Use comparison operators instead
	of wi:: comparisons.
	(tree_int_cst_le): Likewise.
	* gimple-fold.c (fold_array_ctor_reference): Likewise.
	(fold_nonarray_ctor_reference): Likewise.
	* gimple-ssa-strength-reduction.c (record_increment): Likewise.
	* tree-affine.c (aff_comb_cannot_overlap_p): Likewise.
	* tree-parloops.c (try_transform_to_exit_first_loop_alt): Likewise.
	* tree-sra.c (completely_scalarize): Likewise.
	* tree-ssa-alias.c (stmt_kills_ref_p): Likewise.
	* tree-ssa-reassoc.c (extract_bit_test_mask): Likewise.
	* tree-vrp.c (extract_range_from_binary_expr_1): Likewise.
	(check_for_binary_op_overflow): Likewise.
	(search_for_addr_array): Likewise.
	* ubsan.c (ubsan_expand_objsize_ifn): Likewise.

From-SVN: r235719