Auto merge of #98975 - jyn514:unstable_opts, r=wesleywiser

Rename `debugging_opts` to `unstable_opts`

This is no longer used only for debugging options (e.g. `-Zoutput-width`, `-Zallow-features`).
Rename it to be more clear.

cc https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Codegen.20options.20.2F.20debugging.20options

r? `@Amanieu` cc `@nikic` `@joshtriplett`

src/driver.rs

@@ -117,7 +117,7 @@ fn config(&mut self, config: &mut interface::Config) {
         // run on the unoptimized MIR. On the other hand this results in some false negatives. If
         // MIR passes can be enabled / disabled separately, we should figure out, what passes to
         // use for Clippy.
-        config.opts.debugging_opts.mir_opt_level = Some(0);
+        config.opts.unstable_opts.mir_opt_level = Some(0);
     }
 }