debug_printf warning when compiling with c++11. requires constant alternative or (char *) overload

Compiling in c++11 generates borring warnings when using debug_printf("direct string").
to remove this warning, it is possible to define in the header an alternate procedure, just below the closing bracket of __cpluplus test line 80:
static inline void debug_printf(char const fmt[], ...) { debug_printf((char*)fmt); };

this provide an extra procedure, happy with a const direct string.
