Fix Rust Beta warning about deprecated AtomicBool method.

When compiling on Rust Beta, we're generating a warning about:

  warning: use of deprecated associated function
  `std::sync::atomic::AtomicBool::compare_and_swap`:
  Use `compare_exchange` or `compare_exchange_weak` instead

This commit does as advised in the hope of eliminating the warning.

components/places/src/api/places_api.rs

@@ -179,23 +179,19 @@ impl PlacesApi {
     }
 
     pub fn open_sync_connection(&self) -> Result<SyncConn<'_>> {
-        let prev_value = self
-            .sync_conn_active
-            .compare_and_swap(false, true, Ordering::SeqCst);
-        if prev_value {
-            Err(ErrorKind::ConnectionAlreadyOpen.into())
-        } else {
-            let db = PlacesDb::open(
-                self.db_name.clone(),
-                ConnectionType::Sync,
-                self.id,
-                self.coop_tx_lock.clone(),
-            )?;
-            Ok(SyncConn {
-                db,
-                flag: &self.sync_conn_active,
-            })
-        }
+        self.sync_conn_active
+            .compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst)
+            .map_err(|_| ErrorKind::ConnectionAlreadyOpen)?;
+        let db = PlacesDb::open(
+            self.db_name.clone(),
+            ConnectionType::Sync,
+            self.id,
+            self.coop_tx_lock.clone(),
+        )?;
+        Ok(SyncConn {
+            db,
+            flag: &self.sync_conn_active,
+        })
     }
 
     /// Close a connection to the database. If the connection is the write

components/viaduct/src/backend/ffi.rs

@@ -154,15 +154,17 @@ mod callback_holder {
     /// Set the function pointer to the FetchCallback. Returns false if we did nothing because the callback had already been initialized
     pub(super) fn set_callback(h: FetchCallback) -> bool {
         let as_usize = h as usize;
-        let old_ptr = CALLBACK_PTR.compare_and_swap(0, as_usize, Ordering::SeqCst);
-        if old_ptr != 0 {
+        match CALLBACK_PTR.compare_exchange(0, as_usize, Ordering::SeqCst, Ordering::SeqCst) {
+          Ok(_) => true,
+          Err(_) => {
             // This is an internal bug, the other side of the FFI should ensure
             // it sets this only once. Note that this is actually going to be
             // before logging is initialized in practice, so there's not a lot
             // we can actually do here.
             log::error!("Bug: Initialized CALLBACK_PTR multiple times");
+            false
+          }
         }
-        old_ptr == 0
     }
 }