Rollup merge of rust-lang#82736 - spastorino:mir-opt-level-perf-changes, r=oli-obk

Bump optimization from mir_opt_level 2 to 3 and 3 to 4 and make "release" be level 2 by default

r? `@oli-obk`

Author: GuillaumeGomez

src/driver.rs

@@ -83,7 +83,7 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
         // 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 = 0;
+        config.opts.debugging_opts.mir_opt_level = Some(0);
     }
 }