bug#58826: 29.0.50; gud-gdb can't find core file if executable is in a different directory

[Dima Kogan]

Hi. I'm using a bleeding-edge build of emacs, although I think this is a
very old bug.

I just ran a Python program in $DIRECTORY:

  python3 program.py

python3 is in /usr/bin. There was a bug, the program crashed, dumped
core, and I want to debug it. I do this from the buffer containing
program.py (default-directory is $DIRECTORY, which contains program.py
and is NOT /usr/bin)

  M-x gud-gdb
  gdb --fullname /usr/bin/python3 core.sfmviz.py.1807941

It says this:

  /usr/bin/core.sfmviz.py.1807941: No such file or directory.

It works fine from the shell, outside of emacs. The issue is that
gud-gdb is changing default-directory to /usr/bin (where the binary
executable lives). But I never asked for that, and this is unexpected:
I'd expect it to do the same thing as that gdb command would do in the
shell.

Thanks