[clang] [C23] Handle type compatibility for enumerations better (PR #150282)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman can you squash this? (release procedure is a bit different so we prefer to get it pre-squashed).

Sure, but I'm not certain we should have a different merge strategy for main vs release branches so I'd like to understand more about what's driving this. Are we planning on switching all contributions to squashing first? Or is this a temporary thing for release branches?

https://github.com/llvm/llvm-project/pull/150282