[clang] [C] Diagnose use of C++ keywords in C (PR #137234)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> What about `and`, `or`, and friends (which I think are only keywords in C if you include a certain header irrc).

Good call, I'll add those.

https://github.com/llvm/llvm-project/pull/137234