According to https://stackoverflow.com/a/68939636 it is safe to use
__m128i instead.

https://learn.microsoft.com/en-us/cpp/intrinsics/x86-intrinsics-list?view=msvc-170 also uses this type instead

__m128i_u is just __m128i with a looser alignment requirement, but
simply calling _mm_loadu_si128() instead of _mm_load_si128() is enough to
tell the compiler when a pointer is unaligned.

Fixes #1552

PiperOrigin-RevId: 576931936
Change-Id: I7c3530001149b360c12a1786c7e1832754d0e35c