[Issue 12642] Avoid some heap allocation cases for fixed-size arrays

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12642

--- Comment #3 from bearophile_hugs at eml.cc ---
Another comment by Timon Gehr:

> The front end already distinguishes dynamic and static array literals 
> (in a limited form), this distinction should simply carry through to 
> code generation and static array literals should be allowed in @nogc code.

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