[turbofan] Fix silly bug in loop variable analysis.

test/mjsunit/compiler/regress-loop-variable-if.js

Index: test/mjsunit/compiler/regress-loop-variable-if.js
diff --git a/test/mjsunit/ignition/dead-code-source-position.js b/test/mjsunit/compiler/regress-loop-variable-if.js
similarity index 66%
copy from test/mjsunit/ignition/dead-code-source-position.js
copy to test/mjsunit/compiler/regress-loop-variable-if.js
index 95bb9183b880229a703e58503e9aec2a673015aa..ec284e92227d13a63cad7ab8e01826b8111aa558 100644
--- a/test/mjsunit/ignition/dead-code-source-position.js
+++ b/test/mjsunit/compiler/regress-loop-variable-if.js
@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Flags: --turbo-loop-variable
+
 function f() {
-  for (f(x) in []) { f(new f()) }
+  for (var i = 0; i != 10; i++) {
+    if (i < 8) print("x");
+  }
 }
 
 f();