[Issue 20600] C++ header output `-HC` can't write size_t correctly

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20600

Jacob Carlborg <doob at me.com> changed:

           What    |Removed                     |Added
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                 CC|                            |doob at me.com

--- Comment #1 from Jacob Carlborg <doob at me.com> ---
It looks like `core.stdc.config.cpp_size_t` is supposed to be used to get the
correct size and mangling on all platforms. The compiler specially recognizes
`__c_long` and a couple of more symbols related to C and C++ interoperability,
see [1] for all of them.

[1]
https://github.com/dlang/dmd/blob/89d0cd492a5284ab67f665f3014b73905aecb4e2/src/dmd/id.d#L126-L131

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