Rollup merge of rust-lang#53979 - alexcrichton:remove-repr-transparent-atomics-master, r=sfackler

Remove `#[repr(transparent)]` from atomics

Added in rust-lang#52149 the discussion in rust-lang#53514 is showing how we may not want to
actually add this attribute to the atomic types. While we continue to
debate rust-lang#53514 this commit reverts the addition of the `transparent` attribute.
This should be a more conservative route which leaves us the ability to tweak
this in the future but in the meantime allows us to continue discussion as well.

Author: kennytm

src/libcore/sync/atomic.rs

@@ -124,7 +124,6 @@ pub fn spin_loop_hint() {
 /// [`bool`]: ../../../std/primitive.bool.html
 #[cfg(target_has_atomic = "8")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[repr(transparent)]
 pub struct AtomicBool {
     v: UnsafeCell<u8>,
 }
@@ -148,7 +147,6 @@ unsafe impl Sync for AtomicBool {}
 /// This type has the same in-memory representation as a `*mut T`.
 #[cfg(target_has_atomic = "ptr")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[repr(transparent)]
 pub struct AtomicPtr<T> {
     p: UnsafeCell<*mut T>,
 }
@@ -1101,7 +1099,6 @@ macro_rules! atomic_int {
         ///
         /// [module-level documentation]: index.html
         #[$stable]
-        #[repr(transparent)]
         pub struct $atomic_type {
             v: UnsafeCell<$int_type>,
         }