How to check if an array is a manifest constant?

[bearophile]

Jonathan M Davis:

> But there should be no need to worry about whether something is a manifest 
> constant or not.

I'd like in DMD a way to know if something is a compile-time constant. There is a GCC extension that sometimes is able to do it, named __builtin_constant_p:
http://www.delorie.com/gnu/docs/gcc/gcc_81.html#IDX629

Bye,
bearophile