[clang] [clang] Fix crash in concept deprecation (PR #98622)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > Do you have an idea as to why the type location is invalid in the first place?
> 
> Looking at the new test, my guess is that `auto` remains undeduced, so it has nowhere to point out to.

Even when it's undeduced, we should still have a source location for it because the user wrote `auto` somewhere.

https://github.com/llvm/llvm-project/pull/98622