Auto merge of #1438 - AdminXVII:extra-traits-redox, r=gnzlbg

Increase Redox & Relibc support

- Add a lot of constants from relibc
- Fix the timezone not found error found previously on Redox
- Wrap WIFEXITED _et al._ in an unsafe block to match the rest of the API
- Add support for the extra_traits feature and Redox
- Fmt

cc @jackpot51