Auto merge of #50276 - Zoxc:build-cleanup, r=alexcrichton

Misc tweaks

This:
- ~~Add explicit dependencies on `getops`~~
- Fixes the libtest-json test when `RUST_BACKTRACE=1` is set
- ~~Sets `opt-level` to `3`~~
- Removes the use of `staged_api` from `rustc_plugin`
- ~~Enables the Windows Error Reporting dialog when running rustc during bootstrapping~~
- Disables Windows Error Reporting dialog when running compiletest tests
- Enables backtraces when running rustc during bootstrapping
- ~~Removes the `librustc` dependency on `libtest`~~
- Triggers JIT debugging on Windows if rustc panics during bootstrapping

r? @alexcrichton