[Buildroot] Issue with capture of emulator output in runtime test infra

[Edgar Bonet]

Hi!

In response to my suggestion of issuing

    COLUMNS=29999 exec sh

to avoid the command line wrapping, Yann E. MORIN wrote:
> What about actually telling the shell the size we want::
>
>     # stty columns 29999

Good idea: it seems indeed cleaner than starting a new shell. This is
actually telling the kernel's tty driver about the terminal width. The
shell then gets this info from the kernel, via the TIOCGWINSZ ioctl, and
it uses this width unless it is overridden by $COLUMNS.

I just tested on an actual board running Buildroot 2021.08, and it does
indeed prevent the shell from wrapping the lines.

I will send a pull request. May I add your name as Co-authored-by?

Regards,

Edgar.