Fix issue: 5427703 (compareTo), fix parsing of -0.0.

runtime/vm/ast.cc

Index: runtime/vm/ast.cc
===================================================================
--- runtime/vm/ast.cc	(revision 1148)
+++ runtime/vm/ast.cc	(working copy)
@@ -93,8 +93,8 @@
       Double& dbl = Double::Handle();
       dbl ^= literal().raw();
       // Preserve negative zero.
-      const Instance& literal =
-          Instance::ZoneHandle(Double::New(0.0 - dbl.value()));
+      double new_value = (dbl.value() == 0.0) ? -0.0 : (0.0 - dbl.value());
+      const Instance& literal = Instance::ZoneHandle(Double::New(new_value));
       return new LiteralNode(this->token_index(), literal);
     }
   }