[clang] [-Wunsafe-buffer-usage] Fix false positives for constant cases (PR #92432)

[Artem Dergachev via cfe-commits]

https://github.com/haoNoQ commented:

Overall looks great!

I think I see a couple easy improvements, this isn't blocking but let's take a moment to consider them 😊

https://github.com/llvm/llvm-project/pull/92432