Rollup merge of #83277 - spastorino:early_otherwise-opt-unsound, r=oli-obk

Mark early otherwise optimization unsound

r? `@oli-obk`
cc `@tmiasko`

Related to #78496 and #82905

Should I also bump this one to level 3 or 4 or given that is unsound it doesn't matter?.
Probably need to adjust some tests.

compiler/rustc_mir/src/transform/early_otherwise_branch.rs

@@ -26,6 +26,11 @@ pub struct EarlyOtherwiseBranch;
 
 impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        //  FIXME(#78496)
+        if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
+            return;
+        }
+
         if tcx.sess.mir_opt_level() < 3 {
             return;
         }