gud/gdb: dir1/file.cc and dir2/file.cc are the same file

[Nick Roberts]

Klaus Zeitler writes:
 > Symptoms:
 > 
 > When I try do debug a source file (e.q. file.cc), that is a symlink, 
 > emacs says:
 > dir1/file.cc and dir2/file.cc are the same file
 > This would be a nice informational message, if it appeared only once for a
 > file, but unfortunately it gets repeated for every gdb command (step, next,
 > etc.).  Even worse, when I step inside a function in another file, emacs
 > still prints the above informational for the first file with every gdb
 > command I enter.

This should work properly now.

Nick