Make the randomize feature of rustc_abi additive

compiler/rustc_abi/src/layout.rs

@@ -906,9 +906,8 @@ fn univariant<
                 use rand::{seq::SliceRandom, SeedableRng};
                 // `ReprOptions.layout_seed` is a deterministic seed we can use to randomize field
                 // ordering.
-                let mut rng = rand_xoshiro::Xoshiro128StarStar::seed_from_u64(
-                    repr.field_shuffle_seed.as_u64(),
-                );
+                let mut rng =
+                    rand_xoshiro::Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed);
 
                 // Shuffle the ordering of the fields.
                 optimizing.shuffle(&mut rng);