Bug 249040

We use vector XOR in a variety of places in AirIRGenerator to clear a vector value, since XOR is the easiest way to clear/zero a vector on Intel. In some of these places, we create a VectorXor instruction with the SIMDLane of the larger operation. This is often incorrect, however, since vector XOR is only meant to operate over vectors with lane type v128, and passing a different lane type trips an assertion in the macro assembler. In these places, we should explicitly provide a SIMDLane of v128 when constructing the Air instruction.