[turbofan] Properly kill Terminate nodes when removing loops.

test/mjsunit/compiler/regress-491578.js

Index: test/mjsunit/compiler/regress-491578.js
diff --git a/test/mjsunit/compiler/regress-445876.js b/test/mjsunit/compiler/regress-491578.js
similarity index 58%
copy from test/mjsunit/compiler/regress-445876.js
copy to test/mjsunit/compiler/regress-491578.js
index 30e10e56c3ac424fb8843b700bec2af5ded334ac..c27570456c31e9a191fe1f4f1ea17b80f29de98e 100644
--- a/test/mjsunit/compiler/regress-445876.js
+++ b/test/mjsunit/compiler/regress-491578.js
@@ -4,9 +4,12 @@
 
 // Flags: --allow-natives-syntax
 
-function f(x) {
-  while (1) { s++; }
-  while (x) { s++; }
+function foo(x) {
+  if (x === undefined) return;
+  while (true) {
+    while (1 || 2) { }
+    f();
+  }
 }
-
-assertThrows(function () { f(1); });
+%OptimizeFunctionOnNextCall(foo);
+foo();