ARM fix

[SirVer]

I recently compiled nix for my beagleboard black - it went smoothly, but I got two compile errors, both in uio.rs.

The parameter offset to ffi::pread and ffi::pwrite are i32 on my arm. Maybe they should be isize? I am not sure how to express that in rust in a portable manner.

[posborne]

I think using off_t here is the right thing to do but off_t does not have the right value for ARM in your environment. Reading the libc lib.rs, it would appear that off_t should be an i32: https://github.com/rust-lang/rust/blob/8b7c17db2235a2a3f2c71242b11fc429a8d05a90/src/liblibc/lib.rs#L454

[SirVer]

I am sorry, my original bug description was not super great. I was back at my machine today and conjectured a fix real quick in attached pull request.

[carllerche]

Fixed by d980897

[SirVer]

thanks!