[llvm] [NFC] DWARFVerifier: use C-style array instead of brace-enclosed init list (PR #167328)

[Andrei Golubev via llvm-commits]

andrey-golubev wrote:

> What was the warning that you were seeing here? I a surprised no other compilers emit it.

Unfortunately, I do not know the exact one (the original patch wasn't mine). All I found is that it apparently seems to be MSVC bug that doesn't consider `constexpr static auto AllowedForms = {dwarf::Form::DW_FORM_flag_present, dwarf::Form::DW_FORM_ref4};` to be "constant expression" due to the right-hand-side expression (I guess, it didn't like `constexpr auto` + the initializer list `{ ... }`?).

P.S.: actually, this is totally different from what I wrote in PR description!

https://github.com/llvm/llvm-project/pull/167328