zmqpp: exclude old Sourcery PowerPC toolchains that don't have C++0x

zmqpp needs some fairly advanced C++0x features, which apparently
aren't all available in gcc 4.5 used in PowerPC Sourcery 2011.03. So
this commit excludes both this toolchain and the older 2010.09 one.

Fixes:

  http://autobuild.buildroot.org/results/a37/a374e85c714aff26bceaa0df4199bc44a1278f37/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>