vectorcall ABI: require SSE2 According to the official docs at https://learn.microsoft.com/en-us/cpp/cpp/vectorcall, SSE2 is required for this ABI. Add a check that enforces this. I put this together with the other checks ensuring the target features required for a function are present... however, since the ABI is known pre-monomorphization, it would be possible to do this check earlier, which would have the advantage of checking even in `cargo check`. It would have the disadvantage of spreading this code in yet more places. The first commit just does a little refactoring of the mono-time ABI check to make it easier to add the new check. Cc `@workingjubilee` try-job: dist-i586-gnu-i586-i686-musl