Avoid "invalid argument (invalid character)" on non-unicode Windows (#…

…892)

Steps to reproduce and the error message
====

```
> stack haddock basement
... snip ...
    Warning: 'A' is out of scope.
    Warning: 'haddock: internal error: <stdout>: commitBuffer: invalid argument (invalid character)
```

Environment
====

OS: Windows 10 ver. 1709
haddock: [HEAD of ghc-8.4 when I reproduce the error](532b209). (I had to use this version to avoid another probrem already fixed in HEAD)
GHC: 8.4.3
stack: Version 1.7.1, Git revision 681c800873816c022739ca7ed14755e85a579565 (5807 commits) x86_64 hpack-0.28.2

Related pull request
====

#566

haddock-api/src/Haddock/Interface.hs

@@ -84,6 +84,7 @@ processModules
 processModules verbosity modules flags extIfaces = do
 #if defined(mingw32_HOST_OS)
   -- Avoid internal error: <stderr>: hPutChar: invalid argument (invalid character)' non UTF-8 Windows
+  liftIO $ hSetEncoding stdout $ mkLocaleEncoding TransliterateCodingFailure
   liftIO $ hSetEncoding stderr $ mkLocaleEncoding TransliterateCodingFailure
 #endif