0.2.172 is broken on hurd

[SteveLauC]

See the CI log there: https://github.com/nix-rust/nix/actions/runs/14485766160/job/40630925622?pr=2632

error[E0412]: cannot find type `fpos_t` in this scope
   --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.172/src/unix/mod.rs:647:49
    |
647 |     pub fn fgetpos(stream: *mut FILE, ptr: *mut fpos_t) -> c_int;
    |                                                 ^^^^^^ help: an enum with a similar name exists: `fpos64_t`
    |
   ::: /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.172/src/unix/hurd/mod.rs:229:1
    |
229 | pub enum fpos64_t {} // FIXME(hurd): fill this out with a struct
    | ----------------- similarly named enum `fpos64_t` defined here

error[E0412]: cannot find type `fpos_t` in this scope
   --> /home/runner/.cargo/registry/src/index.crates.io-[194](https://github.com/nix-rust/nix/actions/runs/14485766160/job/40630925622#step:5:198)9cf8c6b5b557f/libc-0.2.172/src/unix/mod.rs:650:51
    |
650 |     pub fn fsetpos(stream: *mut FILE, ptr: *const fpos_t) -> c_int;
    |                                                   ^^^^^^ help: an enum with a similar name exists: `fpos64_t`
    |
   ::: /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/libc-0.2.172/src/unix/hurd/mod.rs:229:1
    |
229 | pub enum fpos64_t {} // FIXME(hurd): fill this out with a struct
    | ----------------- similarly named enum `fpos64_t` defined here

I believe 0.2.171 still works

[tgross35]

This was changed in 872642a, the struct in unix/mod.rs probably needs to !(linux && gnu) rather than only !gnu. I'll put up a fix tomorrow if nobody beats me to it.

Thanks for the report!