[clang] [Serialization] Stop demote var definition as declaration (PR #172430)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > I'd like to land this in two weeks if no objections come in.
> 
> Clang 22 branches in a few days, and this should not land before that IMO. Especially given that there was no discussion (that I'm aware of) about breaking the previously valid AST invariant following:

+1, I don't think this change should land for Clang 22; this is changing a long-standing invariant and my experience on the C23 side has been that this invariant is still being assumed in a fair number of places in the compiler.

https://github.com/llvm/llvm-project/pull/172430