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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

After talking with Erich offline, I've updated the implementation to use a binary_search. The pointers are being cast to `uintptr_t` so that the `llvm::sort()` isn't operating on unrelated pointers.

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