Temporarily revert to NonZeroUsize in rustc-abi to fix building on stable

compiler/rustc_abi/src/layout.rs

@@ -2,7 +2,6 @@ use std::borrow::{Borrow, Cow};
 use std::cmp;
 use std::fmt::{self, Write};
 use std::iter;
-use std::num::NonZero;
 use std::ops::Bound;
 use std::ops::Deref;
 
@@ -11,8 +10,8 @@ use tracing::debug;
 
 use crate::{
     Abi, AbiAndPrefAlign, Align, FieldsShape, IndexSlice, IndexVec, Integer, LayoutS, Niche,
-    Primitive, ReprOptions, Scalar, Size, StructKind, TagEncoding, TargetDataLayout, Variants,
-    WrappingRange,
+    NonZeroUsize, Primitive, ReprOptions, Scalar, Size, StructKind, TagEncoding, TargetDataLayout,
+    Variants, WrappingRange,
 };
 
 // A variant is absent if it's uninhabited and only has ZST fields.
@@ -328,7 +327,7 @@ pub trait LayoutCalculator {
 
         Some(LayoutS {
             variants: Variants::Single { index: VariantIdx::new(0) },
-            fields: FieldsShape::Union(NonZero::new(only_variant.len())?),
+            fields: FieldsShape::Union(NonZeroUsize::new(only_variant.len())?),
             abi,
             largest_niche: None,
             align,