Improve the detailed error message for E0432
Improve the detailed error message for E0432

The command-line error message for E0432 does mention the possibility of
missing the `extern crate` declaration, but the detailed error message
for it doesn't.

Fixes #29517.

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