Selected XT and AT clones can use either their built-in FDC controller or an external one (the IBM AT and Compaq AT machines don't support booting from a 1.44M floppy so this makes the external floppy useful).
Added the FDC to the Adaptec AHA-154xCF ("2" variant) and defaulted to None to keep compatibility with existing FDC's.
- 86Box's own headers go to /86box
- munt's public interface goes to /mt32emu
- all slirp headers go to /slirp (might want to consider using only its public inteface)
- single file headers from other projects go in include root
