bug#24125: 25.1.50; Docstring of gud-gdb

[Óscar Fuentes]

The docstring of gud-gdb says:

(gud-gdb COMMAND-LINE)

Run gdb on program FILE in buffer *gud-FILE*.
The directory containing FILE becomes the initial working
directory and source-file directory for your debugger.

/end quote

There is no FILE in the argument list of the function, so this is
confusing, moreover when gdb can be invoked without a program name (when
attaching to a running process, for example.) It is not clear from the
docstring if this case is supported.

System Description:     Ubuntu 16.04.1 LTS

Recent messages:

Configured using:
 'configure --without-toolkit-scroll-bars --with-x-toolkit=lucid'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS LIBXML2
FREETYPE XFT ZLIB LUCID X11

Important settings:
  value of $LANG: C
  locale-coding-system: nil