[Issue 22010] Link error with mutually recursive SumType / struct with opEquals

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22010

--- Comment #2 from Vladimir Panteleev <dlang-bugzilla at thecybershadow.net> ---
(In reply to João Lourenço from comment #1)
> I think this is because it uses `match` internally.

A link error like this should never happen no matter what the code does (unless
it's something intentional like an extern declaration with no definition, of
course.)

> As a workaround fix, removing `const` from `opEquals` solves your issue.

Thanks but this is a reduced example meant to illustrate the compiler bug.

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