[clang] [clang][SPIR-V] Add x86 calling conventions and sse/sse2 for MSVC hosts (PR #227665)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

We seem to be doing fine so far by just having two TargetInfos, and teach Sema to query them as appropriate.  I'm not sure why you think we can't extend that approach to function attributes.

https://github.com/llvm/llvm-project/pull/227665