Rollup merge of #53022 - RalfJung:volatile, r=alexcrichton
Rollup merge of #53022 - RalfJung:volatile, r=alexcrichton

volatile operations docs: clarify that this does not help wrt. concurrency

Triggered by https://github.com/rust-lang/rust/pull/52391. Cc @stjepang @Amanieu

Should the intrinsics themselves also get more documentation? They generally do not seem to have much of that.

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