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

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

If you wanted to do things "properly", you'd probably define `__interrupt` and `__cregister` as attributes in clang/include/clang/Basic/Attr.td .  But at first glance, using macros to ignore `__interrupt` and `__cregister` behaves basically correctly, if you're not actually trying to generate code.  So probably not worth the trouble.

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