[Issue 18084] [REG2.072] tempCString buffer size is unittest-versioned

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18084

--- Comment #5 from Steven Schveighoffer <schveiguy at yahoo.com> ---
This is somewhat how the original worked. I have a feeling the compiler was
having difficulty proving the return wasn't a piece of the object itself, which
is why the latter PR was made.

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