Re-export NonZero signed variant in std

Author: tesuji

Diff for: src/libstd/num.rs

@@ -13,6 +13,8 @@ pub use core::num::Wrapping;
 
 #[stable(feature = "nonzero", since = "1.28.0")]
 pub use core::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU128, NonZeroUsize};
+#[stable(feature = "signed_nonzero", since = "1.34.0")]
+pub use core::num::{NonZeroI8, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI128, NonZeroIsize};
 
 #[cfg(test)] use crate::fmt;
 #[cfg(test)] use crate::ops::{Add, Sub, Mul, Div, Rem};