Fix Windows build following D2588
Fix Windows build following D2588

Commit 8c6a3d68c0301bb985aa2a462936bbcf7584ae9c inadvertently broke the build
on Windows. This restores Windows compatibility.

olsner/ghc,ezyang/ghc,olsner/ghc,ezyang/ghc,olsner/ghc,olsner/ghc,mettekou/ghc,mettekou/ghc,ezyang/ghc,olsner/ghc,sdiehl/ghc,ezyang/ghc,mettekou/ghc,olsner/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,mettekou/ghc,sdiehl/ghc,mettekou/ghc,sdiehl/ghc,mettekou/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,mettekou/ghc,ezyang/ghc,olsner/ghc,shlevy/ghc