Only the code that is in the IDE.
It is now in a package components\lazdebuggergdbmi\ and it is GPL (since it was part of the IDE code, and that is gpl instead of lgpl)
Some of it is IDE specific. But CmdlineDebbugger is good to just launch gdb and communicate.
gdbmidebuginstructions.pp may also be helpful. On top of that you would need to through the code and see what is useful.