message: Move yield_no_wait's flag init out of `unsafe`.
  Turns out core::mem::MaybeUninit::uninit is not `unsafe`!
diff: @@ -13,14 +13,12 @@ impl<S: RawSyscalls> Syscalls for S {
  // -------------------------------------------------------------------------
  fn yield_no_wait() -> YieldNoWaitReturn {
  - unsafe {
  - // flag can be uninitialized because it is not read before the yield
  - // system call, and the kernel promises to only write to it (not
  - // read it).
  let mut flag = core::mem::MaybeUninit::<YieldNoWaitReturn>::uninit();
  - // flag is safe to write a YieldNoWaitReturn to, as guaranteed by
  - // MaybeUninit.
  + unsafe {
  + // Flag can be uninitialized here because the kernel promises to
  + // only write to it, not read from it. MaybeUninit guarantees that
  + // it is safe to write a YieldNoWaitReturn into it.
  Self::yield2(yield_op::NO_WAIT as *mut (), flag.as_mut_ptr() as *mut ());
  // yield-no-wait guarantees it sets (initializes) flag before
  