x86_64: Use %xmmN with vpxor to clear a vector register
Since "vpxor %xmmN, %xmmN, %xmmN" clears the whole vector register, use %xmmN, instead of %ymmN, with vpxor to clear a vector register.
(cherry picked from commit a35a5903)
Since "vpxor %xmmN, %xmmN, %xmmN" clears the whole vector register, use %xmmN, instead of %ymmN, with vpxor to clear a vector register.
(cherry picked from commit a35a5903)