[clang] [Clang][Xtensa] Add Xtensa target. (PR #118008)

[Erich Keane via cfe-commits]

erichkeane wrote:

> For reference, the RFC for the LLVM backend was https://discourse.llvm.org/t/rfc-request-for-upstream-tensilica-xtensa-esp32-backend/65355 . Given there's an LLVM backend, I don't think we need a separate clang RFC? Assuming the target doesn't require any exotic frontend features, we'd inevitably reach the same conclusion as the LLVM backend RFC.
> 
> That said, I am a little concerned that progress on the upstreaming is moving excessively slowly; it's been over two years since the original RFC. New backends don't normally take that long... what exactly has been happening?

I wasn't asking for a separate clang RFC, just I wasn't aware of the previous one!  As you mentioned, it was significantly in the past, so I'd not heard of it/remembered it, and my quick grepping didn't show the backend.

Given the time/progress so far, I wouldn't mind some sort of re-assertion from the community at large that we are a: still interested in this, b: have a dedicated someone willing/able to do the work, which is a criteria for our RFCs

https://github.com/llvm/llvm-project/pull/118008