`std::os::errno` incorrectly has the return type `usize`

[tbu-]

[Jormundir]

Should these kinds of small type changes include a test?

[tbu-]

@Jormundir Don't think so.

@alexcrichton I don't know who to ask for this, but .. should the return type be newtyped?

[alexcrichton]

Currently the plan for errno is to leave it unstable/remove it and possibly add it back in platform-specific modules. If it were a platform-specific API, then it's fine to have its own type on each platform.

I do think that eventually we will grow struct OsError(os::$platform::errno_type) which has nice accessor methods like .code() -> i32 or .message() -> &'static str for example.

For now though, there are no concrete plans to stabilize this API or such a structure.