[clang] [clang] Expand invalid PCM diagnostic (PR #69489)

[David Blaikie via cfe-commits]

https://github.com/dwblaikie approved this pull request.

Looks good.

I wonder how this happened in the first place - that the author of the diagnostic was already adding the 3rd parameter into the arguments but there was no `%2` in the diagnostic text/template... 

It'd be great if we had some kind of checker. I assume we fail if there are too few arguments to satisfy the `%N`s, but maybe we could catch some cases and error if there are too many, too? (I guess in some cases we need it - like we pass 3 things, but depending on one of them, another is unused, etc) - @AaronBallman ?

https://github.com/llvm/llvm-project/pull/69489