[llvm] [ADT] Implement EnumeratedArray with std::array (NFC) (PR #158407)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> Nice. I think the side-effect is that this now allows for 0-sized arrays. Could we add a test for this?

@kuhar I added `static_assert` to disallow 0-sized arrays.


https://github.com/llvm/llvm-project/pull/158407