[clang] [clang] Implement -Walloc-size diagnostic option (PR #150028)

[Vladimir Vuksanovic via cfe-commits]

vvuksanovic wrote:

Thanks for the review. Can someone merge this for me when the CI finishes? The formatting error is due to the indentation of existing code in `Expr.h`.

https://github.com/llvm/llvm-project/pull/150028