Merge pull request #30726 from Microsoft/fix30653

Treat hoisted temp variables as a custom prologue.

tests/cases/conformance/generators/restParameterInDownlevelGenerator.ts

@@ -0,0 +1,9 @@
+// @target: es5
+// @lib: es2015
+// @downlevelIteration: true
+// @noEmitHelpers: true
+
+// https://github.com/Microsoft/TypeScript/issues/30653
+function * mergeStringLists(...strings: string[]) {
+    for (var str of strings);
+}