[Issue 17602] improve message for deprecated enum comparison

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17602

--- Comment #2 from Mario Kroeplin <kroeplin.d at googlemail.com> ---
It is no longer a deprecation warning but an error message.
The error message, however, is still misleading:

---

module a;

enum Status { on }

---

module b;

import a;

enum Status { off }

void main()
{
    Status status = a.Status.on;
}

---

> dmd a.d b.d
Error: cannot implicitly convert expression cast(Status)0 of type Status to
Status

--