support nonzero* niche optimizations

crates/test-utils/src/minicore.rs

@@ -29,6 +29,7 @@
 //!     index: sized
 //!     iterator: option
 //!     iterators: iterator, fn
+//!     non_zero:
 //!     option:
 //!     ord: eq, option
 //!     pin:
@@ -680,6 +681,15 @@ mod macros {
 }
 // endregion:derive
 
+// region:non_zero
+pub mod num {
+    #[repr(transparent)]
+    #[rustc_layout_scalar_valid_range_start(1)]
+    #[rustc_nonnull_optimization_guaranteed]
+    pub struct NonZeroU8(u8);
+}
+// endregion:non_zero
+
 // region:bool_impl
 #[lang = "bool"]
 impl bool {