WIP/RFC patch for Linux termios overhaul

[Florian Weimer]

* H. Peter Anvin:

> It is not even tested, never mind productized, but I would love to get
> some feedback on this approach and implementation.
>
> https://git.zytor.com/linux/glibc.git/commit/?h=hpa/termios

I think it's better to remove <termio.h> stuff from
sysdeps/unix/sysv/linux/bits/ioctl-types.h because it's not really
usable if applications include <termios.h> and <sys/ioctl.h>.

I don't know if we need to keep <termio.h> working, pratically speaking.
Removing <termio.h> and the bad ioctl parts without prior deprecation
warning might be considered a bit rude, but perhaps no one will notice.
We could put the removal into Fedora rawhide if it's separate from the
rest (the new symbol additions).

Thanks,
Florian