Fix undefined behavior when initializing cpu_set_t

While working on implementing a safe abstraction around `cpu_set_t` for the `rsix` crate I've find you're usage of `cpu_set_t`.
However you're usage of it is instant UB because you initialize them when `MaybeUninit::uninit().assume_init()` which is UB by definition.

Comment from bjorn3:
> With UB anything is allowed including compiling it correctly. A future compiler version may replace MaybeUninit::uninit().assume_init() with intrinsics::unreachable(), which makes the syscall trivially unreachable.

Replace their usage with `std::mem::zeroed` witch is the same as using `CPU_ZERO` after initilization.

Author: Urgau

src/linux.rs

@@ -1,12 +1,10 @@
 use crate::Result;
 use ::libc::*;
-use std::mem::{size_of, MaybeUninit};
+use std::mem::{zeroed, size_of, MaybeUninit};
 
 pub fn set_thread_affinity(core_ids: &[usize]) -> Result<()> {
-    #[allow(clippy::uninit_assumed_init)]
-    let mut set: cpu_set_t = unsafe { MaybeUninit::uninit().assume_init() };
+    let mut set: cpu_set_t = unsafe { zeroed() };
     unsafe {
-        CPU_ZERO(&mut set);
         for core_id in core_ids {
             CPU_SET(*core_id, &mut set);
         }
@@ -23,9 +21,7 @@ pub fn set_thread_affinity(core_ids: &[usize]) -> Result<()> {
 
 pub fn get_thread_affinity() -> Result<Vec<usize>> {
     let mut affinity = Vec::new();
-    #[allow(clippy::uninit_assumed_init)]
-    let mut set: cpu_set_t = unsafe { MaybeUninit::uninit().assume_init() };
-    unsafe { CPU_ZERO(&mut set) };
+    let mut set: cpu_set_t = unsafe { zeroed() };
 
     if let Err(e) = _sched_getaffinity(0, size_of::<cpu_set_t>(), &mut set) {
         return Err(From::from(format!(