Issue 10643 - Refused const array struct field initialized with void

https://d.puremagic.com/issues/show_bug.cgi?id=10643

Void initialized non-mutable aggregate members should become instance fields.

Essentially this is a part of [issue 3449](https://d.puremagic.com/issues/show_bug.cgi?id=3449), but because of [bug 11742](https://d.puremagic.com/issues/show_bug.cgi?id=11742), we can fix the issue in advance of the 3449 completion, without breaking any existing code..