Rollup merge of #144010 - xdoardo:bootstrap-warning-optimize-false, r=clubby789

Boostrap: add warning on `optimize = false`

I recently came across a bug that can be traced back to the use of `optimize = false` in `bootstrap.toml` in combination with other settings. Following [this](https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/Missing.20box-related.20symbols.20with.20panic.20.3D.20'abort'/with/528992909) conversation, this PR adds a warning from `bootstrap` when `optimize = false` is used.

I notice that in the same file I edited there are two different styles for warnings (`WARN`, `Warning`). I used `WARNING` because, by happenstance, when testing I got a `WARNING` that I didn't set a change id: let me know if I can unify the styles in the file I edited.

Author: matthiaskrgr