all: add support for windows/amd64

This uses Mingw-w64, which seems to be the de facto standard for porting
Unixy programs to Windows.

testdata/filesystem.go

@@ -33,6 +33,5 @@ func main() {
 		panic(err)
 	}
 
-	print(string(data))
-
+	os.Stdout.Write(data)
 }