[Issue 15828] DMD should refuse comparing unions

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15828

--- Comment #1 from Johannes Pfau <johannespfau at gmail.com> ---
Small correction: std.json has already been fixed in upstream phobos, so I can
just backport that fix for GDC.

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