[turbofan] Fix typing rule for Math.sign.

test/mjsunit/compiler/regress-math-sign-nan-type.js

Index: test/mjsunit/compiler/regress-math-sign-nan-type.js
diff --git a/test/mjsunit/regress/regress-opt-typeof-null.js b/test/mjsunit/compiler/regress-math-sign-nan-type.js
similarity index 73%
copy from test/mjsunit/regress/regress-opt-typeof-null.js
copy to test/mjsunit/compiler/regress-math-sign-nan-type.js
index e4721a18c5e0fb95a3b7cb323f229de9f605b64a..e16eba8c5a3b8ca48f8a055579f6f42289f40a41 100644
--- a/test/mjsunit/regress/regress-opt-typeof-null.js
+++ b/test/mjsunit/compiler/regress-math-sign-nan-type.js
@@ -4,9 +4,11 @@
 
 // Flags: --allow-natives-syntax
 
-function f() {
-  return typeof null === "object";
-};
+function f(a) {
+  return Math.sign(+a) < 2;
+}
 
+f(NaN);
+f(NaN);
 %OptimizeFunctionOnNextCall(f);
-assertTrue(f());
+assertFalse(f(NaN));