Add Spaceball dummy header.
Rename header file.
Its name was previously truncated to the DOS 8.3 filename format.
Make the build platform specific, for now.
Add stub debug utility function.
Make individual compilation units buildable with GCC.
Replace DOS specific header includes and function calls with their POSIX
equivalents where immediately obvious; stub out the rest. Also fix
some minor data type inconsistencies.
Linking still fails due to unimplemented functions (mainly assembler
code and audio library calls).