MFH: r535699

Mark as BROKEN on powerpc64:

./src/configs/include_configs.hpp:2:37: fatal error: configs/power7/config.hpp: No such file or directory

Adding compiler:c++11-lang to USES merely uncovers this error on 12-STABLE;
it does not fix the underlying problem.

Approved by: portmgr (tier-2 blanket)