iot-lab_m3: C++ support

This PR will provide C++ support for iot-lab_M3.
Problem with ```_kill_r``` is resolved by adding ``` __attribute__ ((weak)) ```, thus, if ```_kill_r``` was provided by compiler then we'll use the one provided by compiler instead and ```_kill``` is also implemented with weak attribute.
> I will steal this to ...

no problem =)))