Fix generate_examples build

- Add -march=native to host_copts and host_cxxopts in configure.py
- Make string.h for abstracting string differences at core interpreter level
- Use tensorflow special arg parse instead of flags
- Switch to using tool instead of data for dependency
- Fix python3  compatibility
  + Use six.StringIO instead of StringIO.StringIO
  + Use print_function
  + Properly set binary flags on TempFile's used in toco_convert
- Misc other path fixes

PiperOrigin-RevId: 174717673