Rollup merge of #112619 - jyn514:llvm-reminder, r=Mark-Simulacrum

Suggest bumping download-ci-llvm-stamp if the build config for llvm changes

This will hopefully avoid issues like rust-lang/rust#110474 where the uploaded `rust-dev` component doesn't match the one you'd get if you built LLVM from source.

cc rust-lang/rust#110474 (comment)

Author: matthiaskrgr