Should make strict compilers happy.
Also, make AV_COPY128 use integer operations while at it. Removing the
inclusion of immintrin.h ensures a lot less intrinsic related headers are
included as well, which fixes a clash of defines with some Clang versions.
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: James Almer <jamrial@gmail.com>