[Issue 20208] extern (C++) copy constructor bad mangling for dmd

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20208

kinke <kinke at gmx.net> changed:

           What    |Removed                     |Added
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                 CC|                            |kinke at gmx.net

--- Comment #3 from kinke <kinke at gmx.net> ---
We probably have to emit extern(C++) copy ctors as 2 symbols for non-Windows,
both the C1 ('complete object ctor') and the C2 ('base object constructor')
variant. There's even a third one, C3 ('complete object allocating
constructor'). A similar mess as for the C++ dtors.

The testcase in https://github.com/dlang/dmd/pull/9806 needed the C2 one, so I
assumed it would suffice, but it clearly doesn't: https://godbolt.org/z/qD5Tta

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