Rename AtomicInt and AtomicUint

Change any use of AtomicInt to AtomicIsize and AtomicUint to AtomicUsize

Closes #20893

[breaking-change]

src/libstd/rt/util.rs

@@ -46,7 +46,7 @@ pub fn limit_thread_creation_due_to_osx_and_valgrind() -> bool {
 }
 
 pub fn min_stack() -> uint {
-    static MIN: atomic::AtomicUint = atomic::ATOMIC_UINT_INIT;
+    static MIN: atomic::AtomicUsize = atomic::ATOMIC_USIZE_INIT;
     match MIN.load(Ordering::SeqCst) {
         0 => {}
         n => return n - 1,