[clang] [llvm] [clang] Add support for the c2000 architecture (PR #125663)

[Fangrui Song via cfe-commits]

https://github.com/MaskRay requested changes to this pull request.

(strongly object to the driver mode and option changes. But thanks for proposing the pseudo target RFC, which has potential to support many downstream targets without more custom code in Basic/Targets/Driver.)

(Request changes to ensure that I'll have a chance to look again when this is accepted by others.)

https://github.com/llvm/llvm-project/pull/125663