[clang] [Sema] Fix missing warnings for unused args with invalid printf specs. (PR #158514)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I don't think this is really a good idea.  Typically any time in the compiler we 'continue' after failing parsing like this, we get bogus errors as much as valuable errors.  At worst, we get crashes as the rest of the assumptions in the HandlePrintfSpecifier are going to depend on successful parse.

I'm not convinced as to the value here.

https://github.com/llvm/llvm-project/pull/158514