[clang] [C11] Claim conformance to WG14 N1396 (PR #101214)

[James Y Knight via cfe-commits]

jyknight wrote:

We aren't compliant for assignment either with x87 float/double -- e.g. enable `-O2` on your example.

I think we need to say that we conform except on 32-bit x86 with SSE2 disabled, and link to an appropriate bug. Maybe we'll fix that backend someday. Or maybe not.

https://github.com/llvm/llvm-project/pull/101214