[clang] [clang] diagnose invalid std::tuple_size sizes (PR #159677)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > I mean do we need to use the other patch at all? Why not just backport this one?
> 
> I remembered adding a new diagnostic in a backport patch could cause an ABI break, since we can somehow change the enumeration order in the tablegen files.
> 
> For example, [#139396 (review)](https://github.com/llvm/llvm-project/pull/139396#pullrequestreview-2838187284)

Yeah, we can't backport new diagnostics unfortunately.  

https://github.com/llvm/llvm-project/pull/159677