impl/file_io/posix: added binary mode to fopen() calls.¹
impl/file_io/posix: added binary mode to fopen() calls.¹

1: This doesn't even matter on Linux, but I feel it should be
explicit. Also, I suspect this impl will merge/rename to a
general C impl as it should be supported on other platforms.
Won't know until I explore those platforms.

komiga/togo,komiga/togo,komiga/togo