Fix the nightly futures support

Type Alias Impl Trait (TAIT) seems to now require the type to be
declared in a separate module from where it's used. I don't exactly know
the reasoning for this, but it's fixed now regardless.

src/future/mod.rs

@@ -345,25 +345,25 @@ macro_rules! async_main {
         #[no_mangle]
         pub unsafe extern "C" fn update() {
             use core::{
+                cell::UnsafeCell,
                 future::Future,
                 pin::Pin,
                 ptr,
                 task::{Context, RawWaker, RawWakerVTable, Waker},
             };
-
-            type MainFuture = impl Future<Output = ()>;
-            const fn main_type() -> MainFuture {
-                async {
-                    main().await;
+            mod fut {
+                pub type MainFuture = impl core::future::Future<Output = ()>;
+                pub const fn main_type() -> MainFuture {
+                    async {
+                        super::main().await;
+                    }
                 }
             }
-            static mut STATE: MainFuture = main_type();
+            static mut STATE: UnsafeCell<fut::MainFuture> = UnsafeCell::new(fut::main_type());
             static mut FINISHED: bool = false;
-
             if unsafe { FINISHED } {
                 return;
             }
-
             static VTABLE: RawWakerVTable = RawWakerVTable::new(
                 |_| RawWaker::new(ptr::null(), &VTABLE),
                 |_| {},
@@ -374,7 +374,7 @@ macro_rules! async_main {
             let waker = unsafe { Waker::from_raw(raw_waker) };
             let mut cx = Context::from_waker(&waker);
             unsafe {
-                FINISHED = Pin::new_unchecked(&mut STATE).poll(&mut cx).is_ready();
+                FINISHED = Pin::new_unchecked(STATE.get_mut()).poll(&mut cx).is_ready();
             }
         }
     };