busybox

tidy up O_NONBLOCK usage. use libbb functions in stty.

Added O_RDONLY where improves readability. Note: O_RDONLY == 0,
so it is there even if not specified.

function                                             old     new   delta
stty_main                                           1289    1235     -54

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>