Instead of having a separate module for `arch_consts`, perhaps we could reexport under the same module?

```rust
#[cfg(target_os = "relevant-platform")]
pub mod consts {
    pub use os::arch_consts::ARCH;

    // ...
}

#[cfg(target_arch = "relevant-arch")]
mod arch_consts {
    pub static ARCH: &'static str = "foo";
}
```