Factor out code for setting the console encoding

Moved similar low-level code blocks in Main and GFI for setting the console
encoding to the new module GF.System.Console.

src/compiler/GF/System/Console.hs

@@ -0,0 +1,42 @@
+{-# LANGUAGE CPP #-}
+module GF.System.Console(setConsoleEncoding,changeConsoleEncoding) where
+import System.IO
+#ifdef mingw32_HOST_OS
+import System.Win32.Console
+import System.Win32.NLS
+#endif
+
+setConsoleEncoding =
+#ifdef mingw32_HOST_OS
+    do codepage <- getACP
+       setCP codepage
+       setEncoding ("CP"++show codepage)
+#endif
+       return () :: IO ()
+
+changeConsoleEncoding code =
+    do
+#ifdef mingw32_HOST_OS
+       maybe (return ()) setCP (readCP code)
+#endif
+       setEncoding code
+
+setEncoding code =
+    do enc <- mkTextEncoding code
+       hSetEncoding stdin  enc
+       hSetEncoding stdout enc
+       hSetEncoding stderr enc
+
+#ifdef mingw32_HOST_OS
+setCP codepage =
+    do setConsoleCP codepage
+       setConsoleOutputCP codepage
+
+readCP code =
+       case code of
+         'C':'P':c -> case reads c of
+                        [(cp,"")] -> Just cp
+                        _         -> Nothing
+         "UTF-8"   -> Just 65001
+         _         -> Nothing
+#endif