Rollup merge of #55576 - birkenfeld:opt-level-error-msg, r=cramertj
Rollup merge of #55576 - birkenfeld:opt-level-error-msg, r=cramertj

Clarify error message for -C opt-level

The new levels s and z are not mentioned as possible values.

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