Constant nc::types::TCGETS

pub const TCGETS: i32

These are the most common definitions for tty ioctl numbers. Most of them do not use the recommended _IOC(), but there is probably some source code out there hardcoding the number, so we might as well use them for all new platforms.

The architectures that use different values here typically try to be compatible with some Unix variants for the same architecture. 0x54 is just a magic number to make these relatively unique ('T')