Cmm: constant folding `quotRem x 2^N`
Cmm: constant folding `quotRem x 2^N`

`quot` and `rem` are implemented efficiently when the second argument
is a constant power of 2. This patch uses the same implementations for
`quotRem` primop.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc