[clang] [Sema] Suggest missing format attributes (PR #166738)

[via cfe-commits]

apple-fcloutier wrote:

> Let me make sure I understand. The idea is to emit `-Wmissing-format-attribute` instead of `-Wformat-nonliteral` when possible, otherwise `-Wformat-nonliteral` would trigger. If so, I agree with that.

Yes, exactly (in addition to making -Wmissing-format-attribute a subgroup of -Wformat-nonliteral so that users of -Wformat-nonliteral get it too).

https://github.com/llvm/llvm-project/pull/166738