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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I didn't actually look at this PR closely before I commented.

I think the specific checks clang is doing here have to be part of clang: in particular, clang needs to translate from gcc syntax to LLVM IR asm syntax, and that requires parsing the constraints.  So these checks are necessary, and emitting better diagnostics for checks we need to do anyway seems fine.

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