Eli Zaretskii <eliz@gnu.org> writes:

>> From: Oleh Krehel <ohwoeowho@gmail.com>
>> Date: Mon, 09 Feb 2015 21:33:36 +0100
>> Cc: thibaut.verron@gmail.com, drew.adams@oracle.com, emacs-devel@gnu.org
>> 
>> > AFAICS, it's a simple matter of adding a defcustom to be tested in
>> > gdb-display-io-buffer, causing the latter do nothing if the user says
>> > so.
>> 
>> Just instrumented `gdb-display-io-buffer', it's not the function that
>> makes the *output* buffer pop up when there's new output.
>
> Perhaps gdb-inferior-filter, then?

That's it. Here's the patch.