[clang] [-Wunsafe-buffer-usage] Fold the expression "cond ? E1 : E2" when checking safe patterns, if "cond" is a constant (PR #167989)

[Balázs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

To me the change looks good FWIW.


https://github.com/llvm/llvm-project/pull/167989