Rollup merge of #79986 - GuillaumeGomez:build-help-when-needed, r=Nemo157
Rollup merge of #79986 - GuillaumeGomez:build-help-when-needed, r=Nemo157

Only build help popup when it's really needed

When working on https://github.com/rust-lang/rust/pull/79985, I realized that the help popup was built even when it wasn't needed. This PR only makes the help popup to be built when required.

r? `@jyn514`

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