The present libprintf is a very light printf implementation that is well-suited
for simple bare-metal programs like loadagent; in the present case it overrides
the much heavier printf implementation in newlib.  Programs like the present
loadagent only need printf in order to scribble on the serial console port,
and the most sensible implementation is to have the "character output" function
from the guts of printf point directly to the physical UART output routine, or
a trivial wrapper that turns \n into \r\n.  In contrast, newlib's version would
pull in the complete FILE table infrastructure and malloc etc - maybe OK for
more complex embedded programs that use those facilities for other things under
a bona fide RTOS, but it would be disgusting to pull that stuff in for a
minimal program like ours.

The present printf implementation has been used earlier by the same author
(Michael Spacefalcon) in the StarMON family of PowerPC bootloaders, and in my
MC68x302-based SDSL CPE devices (Hack-o-Rocket and OSDCU).