[clang] [Sema] -Wformat: warn about C23 %b %B when not in C23 language mode (PR #126694)

[via cfe-commits]

SharonXSharon wrote:

> /cc @SharonXSharon

thanks for submitting the fix! A noob question, I wonder in general why does clang choose to warn on the invalid formatter instead of erroring out given it'll be undefined behavior for invalid formatter?

https://github.com/llvm/llvm-project/pull/126694