style: Change some references to raw pointers in some FFI functions

Even tho rust-lang/rust#112337 is IMO a rust
bug, it's easy to work around in our code and it doesn't really affect
expressiveness.

Differential Revision: https://phabricator.services.mozilla.com/D180065

components/style/gecko/arc_types.rs

@@ -23,12 +23,12 @@ use servo_arc::Arc;
 macro_rules! impl_simple_arc_ffi {
     ($ty:ty, $addref:ident, $release:ident) => {
         #[no_mangle]
-        pub unsafe extern "C" fn $addref(obj: &$ty) {
+        pub unsafe extern "C" fn $addref(obj: *const $ty) {
             std::mem::forget(Arc::from_raw_addrefed(obj));
         }
 
         #[no_mangle]
-        pub unsafe extern "C" fn $release(obj: &$ty) {
+        pub unsafe extern "C" fn $release(obj: *const $ty) {
             let _ = Arc::from_raw(obj);
         }
     };