[Issue 20771] va_arg doesn't work for structs with postblits

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20771

Iain Buclaw <ibuclaw at gdcproject.org> changed:

           What    |Removed                     |Added
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                 CC|                            |ibuclaw at gdcproject.org

--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject.org> ---
I don't think this is a druntime bug.  The compiler sets __argTypes differently
for structs with postblits vs. structs without:

```
static if (is(T U == __argTypes))
    pragma(msg, T, " = ", U);
```

Prints:
Postblit = ()
NoPostblit = (int)

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