PR middle-end/43519
* graphite-clast-to-gimple.c (max_signed_precision_type): Use
lang_hooks.types.type_for_size instead of build_nonstandard_integer_type.
When converting an unsigned type to signed, double its precision.
(gcc_type_for_interval): Use lang_hooks.types.type_for_size.
(gcc_type_for_iv_of_clast_loop): Call max_signed_precision_type.
(graphite_create_new_loop_guard): When ub + 1 wraps around, use lb <= ub.