Rollup merge of #38397 - frewsxcv:platform-specific-process-exit, r=alexcrichton
Rollup merge of #38397 - frewsxcv:platform-specific-process-exit, r=alexcrichton

Document platform-specific differences for `std::process::exit`.

Fixes https://github.com/rust-lang/rust/issues/35046.

graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust