[Issue 18958] extern(C++) wchar, dchar mangling not correct

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18958

--- Comment #1 from Manu <turkeyman at gmail.com> ---
wchar_t needs a typedef. It's just an alias, and can't identify it to mangle
properly.
wchar and dchar should be char16_t, char32_t.
DMD doesn't have any C++11 support... so the unit-tests for DMD need
special-case handling.

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