package/lxc: disable broken toolchains on nios2

As discussed with Thomas
http://article.gmane.org/gmane.comp.lib.uclibc.buildroot/100998


only the current toolchains are broken:
"it's better to blacklist the individual toolchains that are known
to be broken, so that if we add another toolchain, we will be able
to see if the same bug happens as well or not."

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>