Make sure that names of temporaries do not clash with real variables.

test/mjsunit/regress/regress-2322.js

Index: test/mjsunit/regress/regress-2322.js
diff --git a/test/mjsunit/regress/regress-2322.js b/test/mjsunit/regress/regress-2322.js
index a60af06148e4aacd8e3d442234aceaf03554bced..1195bab67cb6b9123e93c3bd32135e972799e876 100644
--- a/test/mjsunit/regress/regress-2322.js
+++ b/test/mjsunit/regress/regress-2322.js
@@ -27,5 +27,10 @@
 
 // Flags: --harmony-scoping
 
+"use strict";
+
 assertThrows("'use strict'; for (let x in x);", ReferenceError);
 
+let s;
+for (let pppp in {}) {};
+assertThrows(function() { pppp = true }, ReferenceError);