[clang] [Clang] Add '-Warray-compare' flag for C++ below version 20 (PR #118031)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

Note paper [Remove Deprecated Array Comparisons from C++26](https://wg21.link/p2865) although the lastest version is not public yet. 

https://github.com/llvm/llvm-project/pull/118031