Is there a particular reason you choose to explicitly add CXX flags ('-std=c++11') over CMake's compiler feature support? The later is, in principle, more portable and future proof than hardcoding the flags.
This was asked in an issue earlier today. It's a combination of 1) I didn't even know such flags existed! and 2) I had some compatibility issues with older versions of CMake on my test machines.
I'll look into adding it in the future though!