Yaowu found this function had a compiling issue with MSVC because
of using _mm_storel_pi((__m64 *)(dest + 0 * stride), (__m128)p0).
To be safe, changed back to use integer store instruction.

Also, for some build, diff could not always be 16-byte aligned.
Changed that in the code.

Change-Id: I9995e5446af15dad18f3c5c0bad1ae68abef6c0d