In a future release of the `libc` crate, `libc::timespec` will contain
private padding fields on `*-linux-musl` targets and so the struct will
no longer be able to be created using the literal initialization syntax.

Update the use of `libc::timespec` to create a value by calling
`std::mem::zeroed()` which works with both current versions of `libc`
as well as the future version which contains that change.