Add a Note [Call Arity and Join Points]
Add a Note [Call Arity and Join Points]

as discussed in #13479.

shlevy/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,sdiehl/ghc