[Issue 19321] Unions "may not" have fields with destructors

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19321

--- Comment #2 from Stanislav Blinov <stanislav.blinov at gmail.com> ---
I propose to still make the change, but also add a note about outstanding bugs
(IIRC there was another one concerning assignment of fields). At least that way
the spec will not be misleading.

--