[clang] [C2y] Implement WG14 N3369 and N3469 (_Countof) (PR #133125)

[Alejandro Colomar via cfe-commits]

alejandro-colomar wrote:

> > Thanks @AaronBallman !! I am still working on my patch, so just for learning about Clang internals, I'll try to finish mine, and compare it to yours. :-)
> 
> Sorry for stealing this one out from under you!

No problem.  :-)

> It turns out it was a bit more involved than I expected because I didn't realize how we represented multidimensional VLAs in the type system.

Yep, the GCC patches were also non-trivial; at least for some corner cases.  I had to wait for Martin to patch something unrelated to make it work.

BTW, I'll check all the tests I wrote for GCC, and contribute anything that might be missing here (if any).

> 
> > Sorry for being so slow!
> 
> No worries! I wasn't certain if you had gotten busy or not, and I had some spare bandwidth and wanted to write code for a bit.

:)

https://github.com/llvm/llvm-project/pull/133125