Fix mismatched iowrite* target size and some other compile errors

[whfuyn]

• Fix iowrite* in silly.c to match the target size.
• Fix missing const qualifier in tiny_set_termios.
• Try to fix some other compile errors caused by the tty driver API changes, but I'm not sure whether it has been done correctly.
• sbull and snull are still not compiling. It seems that there are some significant changes that I haven't been able to figure out.

[whfuyn]

Close #81

[qodroi]

Consider maybe applying checks against the kernel version, just like I did in #84,
as many users I believe still have their kernel version under 6.1, etc, and we want to support them.