Add A: 'static to Rc::pin_in and Arc::pin_in

This is required for soundness since `Pin` requires the memory to be
leaked if the `Pin` is leaked.

Author: Amanieu

library/alloc/src/rc.rs

@@ -883,7 +883,10 @@ impl<T, A: Allocator> Rc<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
-    pub fn pin_in(value: T, alloc: A) -> Pin<Self> {
+    pub fn pin_in(value: T, alloc: A) -> Pin<Self>
+    where
+        A: 'static,
+    {
         unsafe { Pin::new_unchecked(Rc::new_in(value, alloc)) }
     }
 

library/alloc/src/sync.rs

@@ -801,7 +801,10 @@ impl<T, A: Allocator> Arc<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
-    pub fn pin_in(data: T, alloc: A) -> Pin<Arc<T, A>> {
+    pub fn pin_in(data: T, alloc: A) -> Pin<Arc<T, A>>
+    where
+        A: 'static,
+    {
         unsafe { Pin::new_unchecked(Arc::new_in(data, alloc)) }
     }