The files in this directory are modified version of "biosboot". The
only difference is in that they perform their I/O via a serial port,
so their preferrable usage is to form bootblocks for systems where the
kernel happens to have an "options COMCONSOLE". Most of the code is
actually shared with "biosboot", and make will not (and should not)
descend into this directory by default. It is in the responsibility
of the user to build these bootblocks instead of the original ones.