Update gid_t and uid_t types for libc

[ian-h-chamberlain]

Fixes #11

Depends on https://github.com/Meziu/libc/pull/6

[AzureMarker]

Edit: needed to cargo update and remove some local Cargo patch lines of course. All fixed

I see some errors:

error[E0308]: mismatched types
   --> /home/mark/media/CLionProjects/rust-horizon/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/std/src/os/unix/process.rs:161:33
    |
161 |         self.as_inner_mut().uid(id);
    |                                 ^^ expected `u32`, found `u16`
    |
help: you can convert a `u16` to a `u32`
    |
161 |         self.as_inner_mut().uid(id.into());
    |                                   +++++++

error[E0308]: mismatched types
   --> /home/mark/media/CLionProjects/rust-horizon/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/std/src/os/unix/process.rs:170:33
    |
170 |         self.as_inner_mut().gid(id);
    |                                 ^^ expected `u32`, found `u16`
    |
help: you can convert a `u16` to a `u32`
    |
170 |         self.as_inner_mut().gid(id.into());
    |                                   +++++++

error[E0308]: mismatched types
   --> /home/mark/media/CLionProjects/rust-horizon/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/library/std/src/os/unix/process.rs:179:36
    |
179 |         self.as_inner_mut().groups(groups);
    |                                    ^^^^^^ expected `u32`, found `u16`
    |
    = note: expected reference `&[u32]`
               found reference `&[u16]`