We need to import 'cast' on Windows
We need to import 'cast' on Windows

This fixes breakage introduced via
47b5b5c2b2c92ba091313c36489588edadceaa9d

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

(cherry picked from commit 11314b936340a0980c27a01400b7dfec2ffdfa42)

nathyong/microghc-ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,nathyong/microghc-ghc,nathyong/microghc-ghc,forked-upstream-packages-for-ghcjs/ghc