Fix the build issue of undefined import self::consts on the loongarch64

[DWwanghao]

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What does this PR do

Fix failed to build for target loongarch64(similar to MIPS) with this error:

error[E0432]: unresolved import `self::consts`
  --> /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/nix-0.26.4/src/sys/ioctl/linux.rs:60:15
   |
60 | pub use self::consts::*;
   |               ^^^^^^ could not find `consts` in `self`

Checklist:

• [x] I have read CONTRIBUTING.md
• [ ] I have written necessary tests and rustdoc comments
• [x] A change log has been added if this PR modifies nix's API