Some possible customizations were already mentioned. The other obvious one is a version of without on-line help. If you feel brave enough remove the definition of the compile time constant HELP from the makefile. A size of the executables will undoubtely go down.
In order to create a version in some other language edit a file lang.h. It contains all messages which may display.
You can adjust to your taste some other points. For example,
what are default requests attached to stepping
commands and what is their status (look in stepping.c for
bpstat(), findcmds(), bpt_list[]).
Which characters are used for requests switching
(see getrequs() in pcs.c).
Some features, like support for functions keys or other symbol
table formats, can be taken out easily without affecting the
whole design.
If you try to recreate with another compiler you should note
that essential parts of this program were written in assembler
and may have to be translated to something your tools can accept.
Here is another point to watch for.
A variable _BLKSIZ sets size of Malloc'ed blocks.
If a library you use supports something similar modify
accordingly.
There are also some constructs in C code,
like a static initialization of a union member (bpt_list
in stepping.c) and an array of size 0 in a definition
of struct symbol in adb.h, which
are accepted by Szozobon C but can give
a hiccup to some other compilers.
These points can be modified without undue strain.
Otherwise the code should be pretty portable, although it is
ST specific by its very nature.