Rollup merge of #46136 - tbu-:pr_werror, r=nikomatsakis
Rollup merge of #46136 - tbu-:pr_werror, r=nikomatsakis

Clarify what `-D warnings` or `-F warnings` does

They set all lints currently on the warning level to `deny` or `forbid`,
respectively.

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