Auto merge of #115795 - Kobzol:opt-dist-custom, r=Mark-Simulacrum

Refactor `opt-dist` to simplify local building

This PR refactors the `opt-dist` tool to make it easier to invoke it locally, outside of CI, and thus simplify building PGO/BOLT optimized `rustc` builds e.g. for distro maintainers. It should also make it easier to run the PGO/BOLT workflow locally e.g. to profile performance or debug issues (looking at you, rust-lang/rust#115554).

Author: bors