package/gnuchess: needs c++

Quoted from ChangeLog:

2013-11-23  Antonio Ceballos  <aceballos@gmail.com>
[...]
    * doc/gnuchess.texi: frontend no longer compiled in C; now in C++.

Fixes
http://autobuild.buildroot.net/results/04e/04e7c14c20f0e056e63a712be3821a3f5c94cff1/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>