Add more missing `{-# LANGUAGE #-}`s to `genprimopcode` output

This is a follow-up to 0620241a
which addressed only the `Prim.hs` output; this commit adds the missing
`LANGUAGE` pragmas for the generated `PrimopWrappers.hs` output as well.

While at it, the redundant `CPP` pragma is removed from the generated
`Prim.hs` file.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>