transpile: Add cross check fields to TranspilerConfig for snapshots

Author: ahomescu

c2rust-transpile/tests/snapshots.rs

@@ -22,6 +22,9 @@ fn config() -> TranspilerConfig {
         fail_on_multiple: false,
         filter: None,
         debug_relooper_labels: false,
+        cross_checks: false,
+        cross_check_backend: Default::default(),
+        cross_check_configs: Default::default(),
         prefix_function_names: None,
         translate_asm: true,
         use_c_loop_info: true,