[clang] [Headers][X86] Enable constexpr handling for MMX/SSE/AVX/AVX512 PMADDWD/PMADDUBSW intrinsics (PR #161563)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

Thanks @markbhasawut - mark this as "Ready for review" when you're done

https://github.com/llvm/llvm-project/pull/161563