[clang] [clang] Improve diagnostics for constraints of inline asm (NFC) (PR #96363)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

If there's some subset of cases that's easy to diagnose, like SSE registers without SSE, maybe we can do that. I mostly care that we don't write a bunch of code to check complicated edge cases, like trying to diagnose if you're using too many registers.

https://github.com/llvm/llvm-project/pull/96363