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

[d-bugmail at puremagic.com]

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

--- Comment #1 from Eduard Staniloiu <edi33416 at gmail.com> ---
Forgot to mention.

I also tested with gdc-9 and everything works as expected (same result as with
ldc).

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