Our system headers have the C++ overloads in them, so GCC is setup to expect that's where they will come from and won't 
provide any of it's own.

6.5.0 system headers do not contain any C++11 support, so they will not have these overloads. 6.6.0 will though.

You can provide your own, like you did for the string stuff. Something like this might work (untested):

#include <math.h>

template<typename T>
double exp(T val) { return std::exp((double)val); }