In pattern synonym matchers, support unboxed continuation results (fixes #9783).
This requires ensuring the continuations have arguments by adding a dummy Void# argument when needed. This is so that matching on a pattern synonym is lazy even when the result is unboxed, e.g. pattern P = () f P = 0# In this case, without dummy arguments, the generated matcher's type would be $mP :: forall (r :: ?). () -> r -> r -> r which is called in `f` at type `() -> Int# -> Int# -> Int#`, so it would be strict, in particular, in the failure continuation of `patError`. We work around this by making sure both continuations have arguments: $mP :: forall (r :: ?). () -> (Void# -> r) -> (Void# -> r) -> r Of course, if `P` (and thus, the success continuation) has any arguments, we are only adding the extra dummy argument to the failure continuation.