Added support for vita target

[nikarh]

Added support for tier 3 armv7-sony-vita-newlibeabihf target.

Rust std actually defines that by target_env = "newlib", but I am not entirely sure about other newlib targets.

If the goal is to align with std, I can change it to that.

[sunfishcode]

I found this code, so it does seem like other newlib targets will use __errno too, so it seems best to follow Rust std here.

[nikarh]

I've updated the PR to use target_env = "newlib".

I didn't remove espidf from cfg. Even though both espidf targets have newlib env in their specs (riscv32imac_esp_espidf and riscv32imc_esp_espidf), it is possible (though highly unlikely) that somebody uses this crate with a custom spec that is not newlib, and a change like that would break this crate for them.

[sunfishcode]

Sounds good.

[sunfishcode]

This is now released in errno 0.3.6.