Don't emit LDummyUse for ArgumentsObject.

test/mjsunit/regress/regress-no-dummy-use-for-arguments-object.js

Index: test/mjsunit/regress/regress-no-dummy-use-for-arguments-object.js
diff --git a/test/mjsunit/regress/regress-347909.js b/test/mjsunit/regress/regress-no-dummy-use-for-arguments-object.js
similarity index 74%
copy from test/mjsunit/regress/regress-347909.js
copy to test/mjsunit/regress/regress-no-dummy-use-for-arguments-object.js
index 90a8e6a759eab76afef1dc968c814bd9d324b147..658d776ea3b80cd00d256a5514603bdb3df1f179 100644
--- a/test/mjsunit/regress/regress-347909.js
+++ b/test/mjsunit/regress/regress-no-dummy-use-for-arguments-object.js
@@ -4,15 +4,17 @@
 
 // Flags: --allow-natives-syntax
 
-var a = {y:1.5};
-a.y = 0;
-var b = a.y;
-a.y = {};
-var d = 1;
+function g() {
+  arguments.length;
+}
+
+var global = "";
+
 function f() {
-  d = 0;
-  return {y: b};
+  global.dummy = this;
+  g({});
 }
+
 f();
 f();
 %OptimizeFunctionOnNextCall(f);