Build script: Add example program makefile.

The example code is now a working program, add it to the unix
makefile tree.
Improve support for 32/64 bit physical addresses in printf().

This change improves the support for physical addresses in printf
debug statements and other output on both 32-bit and 64-bit hosts.
It consistently outputs the appropriate number of bytes for each
host. The %p specifier is unsatisfactory since it does not emit
uniform output on all hosts/clib implementations (on some, leading
zeros are not supported, leading to difficult-to-read output).