[clang] [clang] Constant-evaluate format strings as last resort (PR #135864)

[via cfe-commits]

apple-fcloutier wrote:

Yeah, I'm fixing the merge conflict, unfortunately I got sidetracked _immediately_ after I pushed and found there was a conflict. I'll hopefully get it out by EOD.

https://github.com/llvm/llvm-project/pull/135864