The `c_iflag` and `c_oflag` fields were swapped in the source code which
caused the bit values to be interpreted as the wrong flag. It was a
stupid mistake on my part.
This commit adds support for most of the useful POSIX-defined features.
This will come in handy when dealing with serial terminals that are
implemented in #7260.
Unfortunately, it isn't possible to use `Core::ArgsParser` due to the
oddity of the input format. Most of this code is therefore just data
wrangling and parsing.
