C++11 standard for firmware build

How’s that even though we build against C++11, when using std::to_string(1) I get error: 'to_string' is not a member of 'std'

I get it both with local and cloud compilation. I also added CPPFLAGS += -std=c++11 to my application’s mk.

This is a topic mentioning the same issue: https://gcc.gnu.org/ml/libstdc++/2013-10/msg00245.html