[clang] [clang] Improve `_Alignas` on a `struct` declaration diagnostic (PR #65638)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman you have a preference as to which PR we pursue?

No strong preference, but the author of D141177 seems to have gone silent again so if @jerinphilip is actively working on this patch, I'd say let's go with this one.

https://github.com/llvm/llvm-project/pull/65638