[Issue 24412] No predefined version for 64bit ?!

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24412

--- Comment #5 from Dennis <dkorpel at live.nl> ---
> It's difficult to imagine a case where this could be used where it's a compatibility issue; it's basically for optimisation opportunities, and nothing else.

Since versions are usually about compatibility (i.e. `version(HasFeatureX)
useFeatureX()`), perhaps it would be better to define a 'fast int' type in
druntime, somewhat similar to C's `int_fast32_t` or `intmax_t`, but one that
represents the largest integer type with native math instructions (excluding
SIMD). That would also generalize better to 16 and 128 bit. Would that work?

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