[clang] [Clang] Correct handling of negative and out-of-bounds indices (PR #71877)

[Bill Wendling via cfe-commits]

bwendling wrote:

@kees interesting difference between `0` and `1` in `__bdos()`. You probably know about it, but I was surprised: https://godbolt.org/z/KTeqanjKf

https://github.com/llvm/llvm-project/pull/71877