Tests do not compile on 32-bit architectures

[musicinmybrain]

On i686:

$ git clone https://github.com/eminence/procfs.git
$ cd procfs
$ git checkout v0.17.0
$ cargo test
[…]
error[E0308]: mismatched types
    --> procfs/src/process/tests.rs:461:52
     |
461  |             assert_eq!(v, unsafe { libc::getauxval(k) });
     |                                    --------------- ^ expected `u32`, found `u64`
     |                                    |
     |                                    arguments to this function are incorrect
     |
note: function defined here
    --> /builddir/.cargo/registry/src/index.crates.io-1cd66030c949c28d/libc-0.2.169/src/unix/linux_like/linux/gnu/mod.rs:1340:12
     |
1340 |     pub fn getauxval(type_: c_ulong) -> c_ulong;
     |            ^^^^^^^^^
help: you can convert a `u64` to a `u32` and panic if the converted value doesn't fit
     |
461  |             assert_eq!(v, unsafe { libc::getauxval(k.try_into().unwrap()) });
     |                                                     ++++++++++++++++++++

error[E0308]: mismatched types   
   --> procfs/src/process/tests.rs:461:27
    |
461 |             assert_eq!(v, unsafe { libc::getauxval(k) });
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u64`, found `u32`
    |
help: you can convert a `u32` to a `u64`
    |
461 |             assert_eq!(v, unsafe { libc::getauxval(k).into() });
    |                                                      +++++++

For more information about this error, try `rustc --explain E0308`.
warning: `procfs` (lib test) generated 2 warnings (1 duplicate)
error: could not compile `procfs` (lib test) due to 2 previous errors; 2 warnings emitted

The Rust compiler seems to have good suggestions; I’ll try them and open a PR.