Auto merge of #140464 - oli-obk:successors-mut-perf, r=petrochenkov

Use a closure instead of three chained iterators

Fixes the perf regression from #123948

That PR had chained a third option to the iterator which apparently didn't optimize well

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -757,12 +757,12 @@ impl OpportunitySet {
 
             // Replace `succ` by `new_succ` where it appears.
             let mut num_edges = 0;
-            for s in basic_blocks[current].terminator_mut().successors_mut() {
+            basic_blocks[current].terminator_mut().successors_mut(|s| {
                 if *s == succ {
                     *s = new_succ;
                     num_edges += 1;
                 }
-            }
+            });
 
             // Update predecessors with the new block.
             let _new_succ = self.predecessors.push(num_edges);