[clang] [SYCL] do not support any SYCL standard except 2020 (PR #120258)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> Closing, since this is some incredibly weak argumentation. People rely on this and we generally don't try to break them. This kind of change requires and RFC and obviously a deprecation period assuming there was good reason to drop it, which I can't see here.

Agreed -- this sort of breaking change requires discussion. Please write an RFC on Discourse and get community agreement before continuing with this change.

https://github.com/llvm/llvm-project/pull/120258