[ANNOUNCE] GHC 8.4.1-rc1 available

[Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=)]

Hello Ben,

> As always, do let us know if you encounter any trouble in the course of
> testing. Thanks for your help!

I tried GHC 8.4.1rc1 to understand how SemigroupMonoid and MonadFail
proposals work.

GHC 8.4.1rc1 surely detects Monoid data types if they are not
instances of Semigroup. However, GHC users guide still says that both
-Wcompat and -Wsemigroup are disabled by default. Should we update the
document or am I missing something?

GHC 8.4.1rc does not find Monad data types which define "fail" even
with -Wcompat. Now I understand that
-Wnoncanonical-monadfail-instances is necessary. Why doesn't -Wcampat
include -Wnoncanonical-monadfail-instances?

Anyway, I hope that the proposals will be updated with the concurete
warning flag names so that I can understand them easily.

--Kazu