gdb-create-source-file-list

gdb-create-source-file-list is a variable defined in `gdb-mi.el'.
Its value is

t

Documentation:
Non-nil means create a list of files from which the executable was built.
Set this to nil if the GUD buffer displays "initializing..." in the mode
line for a long time when starting, possibly because your executable was
built from a large number of files. This allows quicker initialization
but means that these files are not automatically enabled for debugging,
e.g., you won't be able to click in the fringe to set a breakpoint until
execution has already stopped there.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.