Auto merge of rust-lang#84802 - jyn514:option-dead-code, r=Mark-Simulacrum

Remove dead code in `rustc_session::Options`

- Don't recompile the same functions for each debugging option
  This reduces the amount of items in the crate by quite a lot.
- Remove unused `parse_opt_list` and `parse_pathbuf_push` functions
- Remove unused macro parameters
- Remove `allow(dead_code)`.

Author: bors