Fix and cleanup can_be_minus_zero computation

test/mjsunit/compiler/minus-zero.js

Index: test/mjsunit/compiler/minus-zero.js
diff --git a/test/mjsunit/regress/regress-crbug-173974.js b/test/mjsunit/compiler/minus-zero.js
similarity index 91%
copy from test/mjsunit/regress/regress-crbug-173974.js
copy to test/mjsunit/compiler/minus-zero.js
index 905bd6058a0ad0fe2ebe10e4c7dafbe9945cbe3b..6efceb54e36834c217732a7974f0c5d2a2cca132 100644
--- a/test/mjsunit/regress/regress-crbug-173974.js
+++ b/test/mjsunit/compiler/minus-zero.js
@@ -27,10 +27,11 @@
 
 // Flags: --allow-natives-syntax
 
-function f() {
-  var count = "";
-  count[0] --;
+function add(x, y) {
+  return x + y;
 }
-f();
-%OptimizeFunctionOnNextCall(f);
-f();
+
+assertEquals(0, add(0, 0));
+assertEquals(0, add(0, 0));
+%OptimizeFunctionOnNextCall(add);
+assertEquals(-0, add(-0, -0));