Fix makefiles so C++ sources can be compiled alongside the C source

this requires main() to be C++ though, so rename the original main,
and add a C++ stub that just calls the original
Compile micropython-wrap test module and register it in main

- requires a few methods to be made non-static so they can be invoked
  by external code
- just call and register initupywraptest() in main since dynamic
  loading for unix is not yet here