bug#31918: 25.3; gud inserts invalid gdb commands

[Eli Zaretskii]

> From: Moritz Wilhelmy <mw-emacs@barfooze.de>
> Date: Sat, 23 Jun 2018 18:13:27 +0200
> 
> I also noticed that Linux console output takes the following form on my
> setup:
> @"console message from the kernel"
> These show up in the terminal, but not in gdb-mi inside Emacs, making
> Linux debugging with gdb-mi a bit cumbersome at the moment.

Does it perhaps appear in the I/O window?

There's also an unused gdbmi-bnf-target-stream-output, maybe you could
use it for this.