[Issue 20141] No builtin version which says if the platform is 64bit

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20141

--- Comment #2 from anonymous4 <dfj1esp02 at sneakemail.com> ---
See also
https://github.com/dlang/druntime/blob/master/src/core/sys/posix/sys/types.d#L45

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